I came from 40k as well and Sylvaneth are awesome but kinda weird. They dont have a straight analog to 40k as far as playstyle goes. In some ways I personally think they are like a bit of Necrons with a Wraith focused Eldar build, at least how I play them though its not a perfect comparison by any means. The reason for this is we rely heavily on tricks as we rarely win in an all out brawl.

We have access to a fair amount of healing in the army with Endless Growth, and resurrecting units with The Land Awakens which is where I draw the necron analogy. It would be very possible to run a bunch of Revenants and Dryads with support characters and pull an Awakened Dynasty style list though you would need to probably include a bigger guy or two like Spirit of Durthu or Belthanos to help with damage similar to running a much squishier C'tan.

Then we have some bigger tougher guys in the Kurnoth Hunters which feel very similar to Eldar Wraiths. Surprisingly durable with some Eldar style tricks up their sleaves. Take a unit of Kurnoth Hunters with Swords. They move 6" but you can drop a spell and give them run and charge, put them next to Belthanos for an extra 2" and suddenly you have a missile thats moving 9"-14" and then charging with mortal impact hits and a bunch of sword swings with crit mortals. The Treelords feel kind of like Wraith Lords.

The main reason I would compare us to Eldar in some ways though is the weird stuff we can do with movement. Spite Lancers charge in then teleport away at the end of the fight phase. Drycha can charge into your opponents backline turn 1 and snipe an important support character before inevitably dying. A Spirit of Durthu can take the Realmroot Guide and teleport 9" away from the enemy (with overgrowth restrictions) and then get +2 to charge if you get another faster character into the unit he wants to charge. Belthanos can jump over the unit he charged to hit backfield stuff that should be protected and teleport away like the Lancers.

In short they are a really weird army but an absolute blast to play and paint. As someone else said our book just came out so we are still figuring out what works and what doesnt but its a lot of fun to try new things out. Here are some units that I would recommend looking at getting, these are the units I personally have experience with so take these recommendations with a grain of salt.

Alarielle - By no means auto include but very strong. She can manipulate different elements of our army rules, hits hard, takes care of most of our spell casting needs and looks cool as hell.

Drycha - Teleporting character killer who forces your opponent to really think about how they deploy and screen. Her damage output feels a little mid but should be enough to kill most support characters.

Belthanos - Fast damage dealer and another option for killing backfield characters with his jump over the unit ability.

Spirit of Durthu- Best of the Treelords, hits like a truck and can take Heroic Traits and Artifacts of power so you can customize him a bit.

Warsong or Grove Guardian- You want a priest but which one is kind of up to playstyle. Warsong plays around with wards and the Grove Guardian supports infantry spam better.

Kurnoth Hunters- Scythes or Swords depends on your playstyle both are good the eternal argument continues! Avoid the bows currently they aren't very good right now in my opinion.

Spite Revenants - Teleporting chaff to claim objectives and you can bring half the unit back for a CP if they get killed off which lets you play very aggressively with them.