Kiffen!
Welcome back, sir! What Ashin said, and Mily's given some great basic info. I will say that for the most part, pvp is fun and the classes seem as balanced as in any other game in that they all have their roles both in pve and pvp, and can do them well.
I wish they'd come out with the Disciple of Khaine, but it doesn't look like it's happening Other than that, definitely tool around with a few. Leveling a character in Aion is no joke and taking a week or two to decide on a class is time well spent.