I am Kesper, a long time casual MOBA and RTS gamer. I played Starcraft II for a while and recently, Heroes of the Storm has captured my interest. I've just begun writing guides, so make sure to give this thing a rating and leave some feedback!

Sgt. Hammer is a ranged specialist and one of the more unique characters in the Nexus. She does absurd damage from long range, at the cost of mobility. When in an organized team that knows to protect their tank, Hammer can dish out unlimited damage and absolutely demolish the opposition. However, a Hammer in a disorganized team who leaves you out by yourself to get ganked by 3 people is a dead Hammer. Hammer will also die very quickly if she is overextended, poorly positioned or caught out with her defensive abilities on cooldown. Additionally, because of Hammer's insane damage potential, she is a prime target to get crowd controlled and focused, which is why she is so reliant on her allies to protect her. Sargent Hammer is a hero that carry her team to a win but requires excellent map awareness to prevent ganks, smart positioning and a cooperative team.

PROS:
-Very high damage output
-Versatile: does great siege and hero damage when played properly.
-Can carry teams to victory

CONS:
-Very squishy, dies very quickly
-Immobile without thrusters
-Hard countered by characters with good gap closers. Also, Stitches's Hook though. If you get hooked, you're dead, and since you're immobile in siege mode, you rely on your team to block for you.
-Incredibly team reliant, need to change playstyle for QM

Spider Mines (Q): Lay down a patch of 3 mines that last for 35 seconds. Mines activate and chase enemies, exploding for damage and slowing.
This gives you vision, which is very important when playing Hammer. Always place mines in bushes to spot enemy heroes coming for a gank. They also don't stop you from moving so you can use them on the run to deter enemies.

Concussive Blast (W): Does damage and pushes back enemies in a cone.
One of your defensive abilities. If someone gets too close to you, this is how you get some distance. Also, it can be used to clear waves if you don't think you'll need it defensively. Helps in escapes too. Just beware of it's deceivingly short range.

Siege Mode (E): Go into siege mode to make yourself immobile but drastically increase your range.
This is what makes Hammer unique. She can become an anchor, rooted in place and immobile but able to dish out the pain from a distance. This ability is especially good for holding down areas where teams are forced engage into you, since you don't have to waste time going into siege mode, and you can blow up enemies while they're walking towards you.

HEROICS EXPLAINED IN TALENT SECTION

Artillery (Trait): Basic attacks do 20% more damage to enemies farther away.
I believe this activates at 3/4 your max range, so keep your enemies far away to do maximum damage.

Thrusters (Z): Activate to increase movement speed by 60% for a short amount of time.
This is your get out of jail free card. This boosts you away from the baddies, and it's your most important defensive cooldown. Unfortunately, it's CD is 30 seconds. Also note that activating this in siege mode will instantly take you out of siege mode and give you a boost.

Hammer's playstyle will vary based on your team. With an organized team, you can teamfight like a god because the enemies should theoretically never touch you. However, in quickmatch you have to be much more careful about when you siege because some people don't know how to protect the tank. There is much to be learned about Hammer and when to use her abilities, when to split push and when to teamfight. Her abilities seem simple, but knowing when to use them takes practice.

Split pushing: Hammer excels at pushing. She can rapidly destroy towers and forts without taking any damage. Siege up and attack towers and forts whenever you have a chance, but don't get caught in a bad spot without thrusters. Constantly watch the minimap, and if you think a gank is coming or if you see one with well placed spider mines, boost a way or just calmly roll out.

Laning: Generally in the early game, don't siege up. You can be caught out and are very immobile, so stay moving! Remember, an out of position Hammer is a dead Hammer. However, as the game progresses, feel free to siege and clear lanes faster. Also, the one exception to the early game rule is if you can siege up with a partner to protect you near some towers, you can get some potshots off. Also, if you can get a good position in lane, feel free to siege and bully your opposing laner away. Just watch out for the gank and keep your finger on the Z key. Just don't get too focused on laning. Your team needs you in teamfights, so don't tunnel vision on lanes.

Teamfighting: Hammer is a DPS god (goddess, actually) if left alone in a teamfight, and usually in quickmatch, the enemy team won't be coordinated enough to rush you, so that's good news! Siege up with the protection of your team once a fight breaks out. You should always be auto attacking and using your Napalm Strike on the squishy assassins or supports. This is a general rule of thumb for most heroes: KILL THE DAMAGE DEALERS AND HEALERS FIRST. DPS characters do all the damage for their team, and if left alone, they will hurt your team a lot. Supports will keep their team alive longer, letting them kill your team more. Warriors are only suppose to get in your face and protect their backline. They should be your last targets. If by any chance you start to lose a teamfight, make sure to boost out of there and save your concussive blast to get some more space.

Ability Usage: Scout bushes with Spider Mines. This helps you escape ganks. DO NOT USE CONCUSSIVE BLAST FOR HERO DAMAGE. It is ok to use it to lane clear IF you don't think it will be needed defensively. However, this is one of your survivability cooldowns, so make sure you save it in fights. Finally, make sure your siege counts. Don't siege up and have to immediately unsiege. It's a huge waste of time, and your team will be missing out on all your DPS. Siege in the correct position the first time. This takes practice. Also, make sure to unsiege preemptively if you don't have thrusters to take you out immediately. Unsieging takes a lot of time you won't have if you're being ganked.

Choices:

Advanced Artillery: Increases Artillery bonus by 10%
I currently don't know if this increases it to 30% or if it's 10% OF 20%, in which case this is trash, but for now this is my top pick.

Lethal Blast: Increased Concussive Blast damage.
Useless. You shouldn't be using this for damage, unless it's for waveclear, and that isn't worth this talent.

Resistant: Crowd control reduced in siege mode.
Sounds good, but you shouldn't be being CC'd attacked so much. Besides, First Aid is a much better talent for survivability because you can use it on the move, and it doesn't only activate in siege mode. Basically, if you're being attacked a little, that's fine because you should be able to live through it, but if you're close enough to the frontline to be CC'd easily, you're positioning is a bit off. Move back. (Unless you're completely dominating and want some more shots on fleeing heroes)

Ambush: Cloak when entering siege mode and deal 100% extra damage on next auto attack.
A lot of fun. This can be kind of handy for sieging up on objectives and surprising the enemy team, but this is really only useful for, well, ambushes, and the only way it's useful there is if you're the only one ganking, in which case you are overextended and out of position. HAMMER DOES NOT GANK. SHE BLOWS PEOPLE UP FROM AFAR.

Regeneration Master Gather regen globes to increase health regen permanently.
Total trash. You shouldn't be taking this much damage, First Aid is far superior, you have to gather the globes which means walking foreward towards the enemy team, when you should be staying at range, and Hammer's health pool is so small that she can be bursted down regardless of this. This talent is useless.

Choices:

Vampiric Assault: Basic attacks heal you for 15% of the damage dealt.
Definitely the best QM choice. This lets you be less team reliant and sustain yourself more in lane and teamfights, at the cost of a bit of damage. Hammer right-clicks a lot, and the 15% will add up quickly.

Focused Attack: Every 10 seconds your next basic attack does 75% extra damage. Basic attacks reduce this cooldown by 1 second.
I love this when I have a strong healer who knows to babysit me. Hammer auto attacks a lot, so you get tons of focused attack damage. However, losing the sustain from Vampiric Assault sucks in QM where you need to be a bit independent.

Maelstrom Shells: Standard basic attack range increased by 20%
Currently I am not sure if this affects siege mode range. If it does, that's awesome. If not, kind of useless, but I would pick Vampiric Assault either way because the sustain is good and otherwise you only have First Aid for sustain, which is on a 60 second CD.

Excessive Force: Doubled knockback distance on Concussive Blast.
Sounds good in theory and it's hilarious to watch, but you should be able to escape when all your defensive cooldowns are off without this, and Vampiric Assault is just better.

Choices:

Slowing Mines Mine slow and slow duration increased.
I personally don't go for mine builds, but this can provide some interesting soft crowd control. Over all though, this is the weakest talent in the tier.

Hyper-Cooling Engines: Thrusters cooldown reduced to 15 seconds and activated automatically in base.
It's close between this one and First Aid. This talent gives you double the mobility and more survivability through escapes. However, after some testing I've come to prefer First Aid. This one really depends on what you want though.

First Aid: Activate to heal for 35% of your max health over 6 seconds.
This lets you have that extra healing to keep you alive if you get jumped, it lets you stay in teamfights even if you are being hit, and it lets you avoid having to go back to base and slowly drive back. Hyper-Cooling Engines does improve your survivability and mobility, but if you're careful with your thrusters you shouldn't really need it, and First Aid is more useful in that case.

Choices:

Blunt Force Gun (BFG), (R1): Shoot a large bullet that damages enemies in a line across the map.
Not gonna lie, this ult is one of the most fun heroics in the game. When you get Orbital BFG at level 20, you can demolish enemy structures without even being there. It's a lot of fun, but the cooldown is like 70 seconds, and the damage is only moderate.

Napalm Strike (R2): Launch a napalm strike that does impact damage and damage over time to enemies standing in it's impact area for 4 seconds after.
This is also a fun ability, only because you can spam it. It only has a 6 second cooldown! This ult does tons of damage if used a lot, and it is more versatile than the BFG because it can do hero damage, siege damage, clear waves, take mercs, zone and do pretty much everything. However, the satisfaction of mowing down a bunch of low health heroes with the BFG cannot be met with Napalm Strike :)

Choices:

Giant Killer: Basic attacks against enemy heroes do an additional 1.5% of the hero's maximum HP.
Great pick on a auto attack heavy hero. Your damage goes sky high with this talent. Also, it's always active, which gives it a leg up on First Strike.

First Strike: After not taking damage for 5 seconds your basic attacks do an additional 25% damage.
If you want to place your DPS maximum in the hands of your team, go for this. 25% extra damage is nothing to sneeze at, especially on Hammer. If left alone, you can seriously wreck some fools, but all it takes is one skillshot or AoE to reset that 5 second timer.

Bullhead Mines: Spider mines do knockback.
Sounds good, but I've never actually picked this, since I read that only the middle mine does knockback. I need to test this, but unless you want a mine build, this talent is weak.

Barricade: Concussive Blast creates a wall that fades after a short amount of time.
This is seriously one of the most underrated talents in the whole game. It can set up some insane plays and tricks. However, it makes you use one of your defensive abilities to do these things, so I personally don't like it. However, the tactical options are amazing.

Choice:

Executioner: Basic attacks do 40% extra damage to stunned, slowed, rooted or silenced targets.
If you have reliable CC on your team, this is 100% the best pick. 40% extra damage is insane, and coupled with Giant Killer or First Strike, you can do absurd damage. Pick this if you have a good Arthas, Jaina or Putrid Bile Stitches on your team. Basically if you have heroes that apply some kind of hard or soft CC a lot, this talent is great.

Mine Field More Spider Mines created.
Use only for a mine build. Duh.

Hover Siege Mode: Move at 50% movement speed in Siege Mode.
This talent lets you move and deal damage without having to unsiege and siege again. All in all, this is a very versatile talent. Just make sure you remember that you can unsiege!

Graduating Range: Range periodically increases when remaining in siege mode.
This talent forces you to remain immobile, which I don't like. However, if you're going to be sitting somewhere for a while, like on a temple (after the big mob is gone so it can't push you) on Sky Temple, this can be really good.

Stoneskin: Activate to gain 30% of your max HP as a shield.
Meh. Hammer's HP pool isn't enough for this to be too good. Only pick it if you're dying A LOT.

Orbital BFG: BFG orbits around the map periodically.
Must pick if you got the BFG in the first place. If you don't get this, it's a waste of an ultimate because the only useful thing the BFG can do is consistent siege damage.

Advanced Lava Strike: Increased range and impact damage of Napalm Strike.
Pick if they have Imposing Presence. Otherwise, GET THE NEXUS FRENZYYYYY. It's just better. Napalm Strike is fine on its own.

Fury of the Storm: Basic attacks splash.
This is really only useful for lane. Hammer already has good lane clear, so this is redundant.

Nexus Frenzy: Increase basic attack speed and range by 20%
WHAT? You gave the longest range and highest damage auto attack character a buff in attack speed and even more range. Blizzard, you've created a monster. PICK ALMOST ALL THE TIME.

Early Game: Remain mobile, don't get ganked. Focus on gaining XP. If you get a good position, siege up for some potshots on towers or to bully enemy heroes out of lane.

Mid Game: Split push and do as much siege damage as you can, but make sure you keep an eye on your map for ganks and so you can be with your team for teamfights.

Late Game: Push down towers and forts, but be ready to teamfight. Basically the same as the mid game but with higher death timers, so watch your positioning!

Sgt. Hammer is possibly the most team reliant hero in the Nexus. She is immobile and vulnerable to ganks. However, when played correctly with good map awareness and positioning, Hammer (with the help of her team) will absolutely demolish anybody within the circle of her attacks.