Battlenet name is Malbek#1689 - I am a Rank 1 (currently 3500 mmr) player that mains the support role, with Tassadar at the top of my favorites. I played Heroes of the Storm for a few months during the technical alpha, and then picked the game back up a few months after official release. I started placement matches as soon as I hit lvl 30, was placed at rank 9, and then ranked up to 1 within just a few days playing (and carrying with) mainly Tassadar. Before HotS I played League of Legends for a few years, and DotA for a couple years before that.
Tassadar is a tier 1 support that focuses on damage mitigation (shields) and vision control. Like many heroes, he has a primary talent path that I recommend, but also has a couple alternatives you may choose in particular situations. He is typically best paired with another healer on the team such as Tyrande or Li Li, but I have won plenty of Rank 1 games as solo support T*** with my primary build.
Plasma Shield is arguably what makes Tassadar so strong. At 40 mana and a 5 second cooldown, it is a spammable ability that has great talents you can choose to go with it. It is 50% stronger when cast on an ally, so you get much more value from it if you let your allies do the tanking and spam it on them instead of having to use it on yourself. It is also stronger than every other single-target heal in the game, not including Heroic abilities.
Psionic Storm is an AoE damage ability that does damage in a small area over 3 seconds. There are some good talents to support it if you choose to build DPS, but by itself it really doesn't do much damage. The best uses for this ability are to clear waves (Takes 2), and to interrupt enemy champions from channeling objectives (Tributes, Dragon Knight, Altars, etc).
Dimensional Shift is one of the best escape / get out of jail free cards in the game. Tassadar doesn't stealth - he completely phases out of the game for 1.5 seconds. That means he can walk through Nazeebo Zombie Wall, dodge Kael'thas Pyroblast, juke opponents, and walk through body blocks. Since you are not stealthed, there is no blur around your character like Nova - you are completely invisible to opponents. It does have a long (20 second) cooldown though, so use it only when you absolutely have to, and make sure you always have enough mana to cast it!
Archon is Tassadar's first Heroic ability. It gives you a large shield, and makes your auto attacks do more damage & splash. If you are going for DPS, or are not very good at Force Wall, then this is the heroic to opt for. It can be dangerous because it puts you closer to the combat, and may force you to spend your Plasma Shield on yourself instead of allies for that 50% boost.
Force Wall is possibly my favorite ability in the game. If you have played Starcraft, it is very similar to the sentry's force field ability. It has a very short (12 second) cooldown, and has a lot of potential to make plays with. You can use it to trap enemies that are running away, to disengage and prevent the enemies from chasing, and just to create space in a team fight between enemies and allies. With such a short cooldown, it is okay to spam, and it very often gets my team kills that we wouldn't normally be able to get, and saves allies by putting a Force Wall between them and enemy melee hero.
Oracle is Tassadar's combat trait (D) and very good for revealing stealth, bushes, objectives, and extra vision in general. Nova and Zagara players especially hate this ability. It does have a long (40 second) cooldown, so use it conservatively - such as when you are fighting for an objective, or pushing on the enemy side of map. Also good for clearing Zagara Creep Tumor and Abathur Toxic Nest.
I have found Conjurer's Pursuit is the best level 1 talent because mid-late game you need to be able to spam your shields on allies during and before fights, and also always have mana for your Dimensional Warp and Force Wall. While regeneration globes are going to be very important for you with this talent, don't risk suicide when trying to collect them. If there are two or more enemies standing on top of the globe, just let it go.
Overload Not Recommended/Situational
I have never chosen this talent before to be honest. I could maybe see it as viable if you were going a straight dps build and were laning against someone like Raynor or Zagara, but I wouldn't recommend this talent normally. You are giving up good mana regen if you opt for this talent.
Psi-Infusion Don't Choose
For mana regeneration, I prefer Conjurer's Pursuit over Psi-Infusion. This talent may be an okay choice if you build Second Strike and Rewind as well, but my main problem is that it doesn't grant any mana outside of combat. Tassadar needs good mana regen outside of combat as well because he wants to always have his Plasma Shield up on all allies. It is "safer" mana regen, because you don't have to walk out into lane to get regen orbs for conjurers pursuit. But, Tassadar has a safe enough kit that collecting orbs is rarely a problem.
Reinforce Structure Not Recommended
Reinforce Structure is not a terrible talent, but not the best either. Preventing your structures from dying is a good thing, and this talent is effective against objectives like bosses and cannons. One problem is there is no guaranteed value from this talent. If your lane is never pushed up to your towers, or if your enemies cant cap any objectives (This is good - means you are probably winning), then you wont get much value from protecting your structures, and it will have been a wasted talent.
Leeching Plasma Recommended
This is the talent I most commonly choose because of how well it combos with Khala's Embrace. By itself, it will give your Plasma Shield target 30% lifesteal (Very good with champions that auto attack a lot, like Raynor. In combination with Khala's Embrace though, you can give your whole team 30% lifesteal for as long as their Plasma Shield is up. Which, if you are playing correctly, is going to be all the time. This talent is a big reason why Tassadar doesn't always need a healer on his team.
Mental Acuity Situational
I pretty much only choose this talent if we already have a healer on the team, and if the opponents have a Nova or Zeratul (or Nova and Zagara). It reduces your Oracle cooldown to 20 seconds, so you can use it a lot more often and establish vision control and lock down stealth heroes.
Healing Ward Situational
Healing Ward is a decent talent if your team doesn't have a healer, and if it's a map with a lot of long team fights, such as Cursed Hollow and Blackheart's Bay. I still typically prefer Leeching Plasma though, unless you don't have any auto attack heroes on your team such as Raynor.
Promote Don't Choose
Promote could be used to help push lanes and establish some map control. However, I would not recommend taking this talent. It's useless in actual fights, and is easily cleared.
Khala's Embrace Recommended
This is my preferred support talent here. Mid-late game, you will be able to have it a shield up on all of your allies at all times because of Conjurer's Pursuit and also combos well with Leeching Plasma to give your whole team 30% lifesteal. This ability helps mitigate some of Nova's burst, and essentially gives your whole team extra HP for team fights.
Deep Shift Don't Choose
Personally I think 1.5 seconds with Dimensional Shift is long enough to get me back into a good position, especially once we also talent Prescience. So I wouldn't recommend this talent unless you very often find yourself in bad position.
Static Charge Situational
This is the talent to go with if you are opting for a DPS build. Tassadar's basic attacks by themselves are one of the lowest dmg basic attacks in the game, sadly. If you combo this with Archon and Second Strike, you will have a lot of DPS to add to your team. I would also consider if I have another good healer on my team, and need a little extra DPS on my team.
Calldown: Mule Not Recommended/Situational
With other great talents at this level, I wouldn't recommend the mule. A lot of it is the same reason I explained above with Reinforce Structure. It doesn't add anything to team fights, and has the potential to lose a lot of value if your structures aren't taking consistent damage. If you don't think you will need Prescience, then mule could be a good talent on Blackheart's Bay though.
Distortion Beam Don't Choose
This is the talent I would probably least recommend at this level. Your basic attacks slow enemies by 20%, but this requires you to be constantly using your basic attacks to be useful. As Tassadar, unfortunately your basic attacks are not consistent.
This is the talent I recommend most of the time. It has a separate cooldown from your Dimensional Shift, so as soon as your Prescience procs, you can use Dimensional Shift right after. It also works in combination really well with Dimensional Warp, my preferred lvl 16 talent to heal you to full. This talent also lets you play a little more dangerously, and put yourself out of position to make plays with Force Wall and such, because you are guaranteed safe.
Scryer Not Recommended/Situational
If you are never getting caught, and feel very safe in the game, then you can consider Scryer. I very rarely choose this talent, but if I did, it would be because I already got Mental Acuity at lvl 4, and am facing a Nova/ Zagara/ Abathur. The extra duration will allow you to clear more creep/mines, and gives you vision control for slightly longer. It also gives 20% movespeed which may help put you into better position for Force Wall or for disengaging.
Shrink Ray Situational
I will take Shrink Ray occasionally, but only if the opponents have a high damage melee assassin that dives our back line. This ability gets a lot of value against opponents such as Zeratul, Illidan, and Sonya by negating 50% of their damage and making them easier to kill. It can also be used to slow movement speed on enemies that are trying to disengage.
Evasive Shielding Not Recommended/Situational
This talent could be viable if your back line is getting dove a lot, to give your squishies some extra move speed to kite with. It will also give your team more ability to chase and to disengage. Unfortunately this talent only lasts 5 seconds, so does not combo with Khala's Embrace to give a permanent move speed boost. If you didn't take Prescience at level 13, then this could be a good option.
Dimensional Warp Recommended
If you took Prescience at level 13, then I would definitely recommend Dimensional Warp to go with it. The healing and move speed with proc on both your Prescience and your Dimensional Shift, so you can be healed back to full almost instantly. In between fights, you can use your Dimensional Shift to self heal with this talent instead of going back to fountain as well. If you need to initiate a fight or a speed boost to get a good Force Wall off, pop your Dimensional Shift for the movespeed boost you get from this talent.
Resonation Don't Choose
Your psionic storm will slow targets within the AoE for 1 second. I don't really see any situation where this talent is a viable option.
If you picked up Archon at level 10, then this is probably the storm tier talent for you. Increasing your shield and attack range will make you a little safer, and the damage boost is good of course.
Force Barrier Situational
Although I love Force Wall, I rarely pick up Force Barrier. While a longer cast range and 1 second longer duration is definitely good, there isn't guaranteed value from it this late in the game. Consider this if you have a strong healer already, and expect the game to last long enough that your Force Walls will still be vital.
Storm Shield Recommended
This is my preferred support storm tier talent. The range on this ability isn't super big, so be sure to get into a position where you can cover your whole team with this shield. Depending on your team comp, it can add anywhere between like 3k-6k health to your team as a whole, and can turn the tide in team fights.
At low rank, Tassadar's win rate is not statistically very high. He takes a lot of skill to play well! But you will see at high level, he has a much higher win percentage. The talents statistics pool together both high MMR and low MMR.