it's the only MMO (aside from guild wars, which is only an MMO by claim) with a format for any semblance of competitive pvp. while it's a mess as far as balance is concerned, it's steps ahead of zerging around in a group and talking trash about ambiguous victories -_-
This. Anyone who says different hasn't played high rated arena.
About Aion, it's decent and will probably do ok sales wise, but it's too grindy and the endgame PvP is going to be zerg vs zerg aka boring. I preordered it a while ago mainly to try the beta. I'll probably play my free month or whatever.