I bought it over the week-end, so I can give it a quick review.
Looks: It looks great. The character creation is very well done, you can look as gorgeous or as demonic as you like, and there's a lot of variety in heights, styles, haircuts, etc... I spent a good 20 minutes creating my girl Ranger, and I enjoyed so much that I also created a guy on the Evil side, which I'll probably never play.
The game itself looks very nice. The mobs, the landscape, the cities all range from "very nice" to "breathtaking".
Feel: It feels like WOW. The interface is the same, the mechanics are similar, there's nothing ground-breaking there. It's fluid, it feels real, and I played it for 5 hours straight without feeling like throwing-up. I can't say the same about Warhammer, which was fun but which I couldn't play for more than a couple of hours straight.
Gameplay: It reminds me of vanilla WOW, just a bit harder. Mobs take a while to solo, and forget about taking on more than 2 at a time, at least in the early levels. I died lots of time, and while there is a death penalty, it's not too harsh.
Questing is fine, although for the first 15 levels you are pretty much taken by the hand and led through the quests. There is very little room for exploring, or for not doing things the scripted way. But some touches are nice, little cut-scenes, your character taking out a fan if you wait too long, it's pretty cute. Having said that, if the game stayed that way through-out, it would be super boring. The fun starts at around 20-25 when you get to go the Abyss. And, as much as it pains me to admit it, my Ranger is only level 15, so I can't comment on that. There has been 0 grinding so far, although there isn't an abundance of quests either. If you should skip a couple of quests, grinding would probably be necessary. Having said all that, PvE is a side-show of this game, which is designed around PvEvP. Which is just as well, since the PvE is very basic. The quests are all the same, kill X, gather Y, there's nothing else. Which is fine by me, but might not be for some who enjoy running around playing UPS man. Also, it's a bit slow. Mobs take a long time to kill, and the levelling feels a bit long. Crafting seems ok, although I've done little of it so far.
Overall, it feels nice and it looks good. I'll reserve my judgment until I reach 20-25, and try out the Abyss, PvEvP, and instances. If these are fun and well-done I'll continue, if not I'll quit. I do think Aion is meant to be played with some friends, or as part of a guild, as it can be a bit tedious to level alone in some parts. And, well, obviously for PvP.
The wings are fun, but it's not that amazing either. At least so far, maybe they do give an extra dimension to PvP, dunno yet.
So yeah, pretty good so far, but I'll wait another 10 levels before deciding whether to stick to it.