Well, what is good to get? The codex. That will give you an idea of what the army is about fluff-wise, from there you can see what units you like.
Eldar are fast, have hell of a lot of shots, and its' specialized cc units are very good. And they're much more durable than Dark Eldar. note that if you join GTs, your sportsmanship scores would suffer because many people see the Eldar army as a "cheesy" army.