Hello there!
I am KingRat, started playing HotS in late november during the alpha, and this is my first Guide, hope it will help you, dear last souls with the newest hero, Sylvanas Windrunner.

While I am not the brightest and greatest player, I hope this guide will help others and I am open for suggestions :)

While she is offically a specialist, during the first day of release she proved to be great asset in any teamfight and can easily chase as good as Illidan.

Basics
So what you have to know about this hero?
She is fragile. To stay in second line while you can. Don't go in 1v1 fights while there's chance that anyone else will join the fight.
The most wonderful thing is, she can stun forts, turrets, minions and merceneries expect boss. So you simply can't hit one building, stay in the middle of the lane, while you hit both towers.

Escape
Think before trouble happens - even her Haunting Wave seems a good way to escape, it's not as easy as you would think. While Valla can easily dodge, you have to wait till the banshee's arrive at the location and press E again.
The good thing is: it passes through objects. So you can dodge through walls, trees, buildings, escaping for sure.

Teamfight
This is where Sylvanas shines the brightest, even she is a rotting piece of flesh. Sorry guys, that's the truth.
While the damage is relatively low, her ultimate, wailing arrow can silence the whole team, interrupting skills, preventing heals.
As I mentioned, she is a good chaser, if you want to. See later at talents.

I choose Lost Souls. See tier 6. In addition, it proves to be most useful at later game, around 5+ minutes, where teamfights become more regular, and waves become more crowded. The effects spread, infecting tens of minions at the same time, dealing damage over time and makes much easier to get rid of them - gaining exp. faster.

With the wind is a so-so choice, improving range can make you stay away from other heroes, makes chases easier.

The other two talents I would not recommend: only, if you are sure you will have the opportunity to solo lanes.

To be honest - after a day of play, I am not sure with this one.

Paralysis - greats for assault, making camps easier with improved stun duration. Helps team with blocked building, while you can still take care of other heroes.

Envenom - as good as other heroes'. Good finishing move and weakining enemy heroes.

Ranger's ambush - the talent I found most useful. If you are not afraid of dying (and you should be), you can simply dive in, make the support run, while the others attack you. The more useful way is during chase and merc camps, after the teleport activated, it will refresh your Q.

While I saw many to choose Shade form, I would recommend you Life Drain. In massive waves, you can fill your health easily. Great during escapes.

Wailling arrow - as I mentioned in the first chapter, most useful asset of the teamfights. Silences whole team, while dealing mediocre damage.

Possession - saw no one choosing it, neither did I. Keep in mind - it has 4 seconds cooldown. Can turn crowds against the enemy, increasing lane size - but probably mostly useless if they pay a little bit of attention.

Splinter shot - again, great at clearing waves, bounces of heroes too, dealing massive damage to a whole team. You can roam the map and close up if you left behind with exp.

Overwhleming Affliction - again, chasing and 2v2 fights. Stacking up to 30% slow is insane.

Absolutely Cold Embrece. It just goes too well with Tier 1 and Tier 3 - while it has almost no use at laning, it is great at offense and teamfights. It has spreading vulnibarity, increasing every damage taken by 25%. Can easily turn the tides of battle and you can go through bases like a steamroller on lollipops.

Honestly? Your choice. If you took Possession, you absolutely have to choose the second tier of it. You will turn merceneries, improving damage and health. Sadly, doesn't work on bosses.

Bolt of the Storm - well, improves your mobility and survival chances.

Deafening Blast - makes the enemy team handicaped bunch of heroes with doubled silence time.

Well, thank you for reading my first guide, I am open to any suggestions and advices.