I realize it plays differently, but again, I'm not sure that should be an area of concern. The fact is that the MMO framework is all there, but it's been improved upon, and this includes the combat. I don't know, maybe I'm crazy, but I'm pretty sure that many current MMO players would enjoy more involved, fluid combat. Not to mention I feel that GW2 has the potential to attract a wider audience to MMOs a hell of a lot more than WoW has based on combat alone (active vs. rotations/bar watching).
To address the desire to become "the next WoW": sure, WoW sales would be great for ArenaNet. However, that's not their immediate goal — sure, in time, they would love to build a player base that could compare to WoW's, but I think we'd all be a lot better off if fans for both GW2 and SW:TOR stopped talking about WoW killing. WoW will die on its own at some point... it's not going to last forever. Whether Guild Wars 2 contributes to that or not, most of us are confident that it will draw a respectable amount of players to the game, whether they be full-on players or players that might play a subscription MMO on the side.
This is totally lame, but if you're at all paying attention to primetime TV right now, it's like "The X Factor" vs. "American Idol" comparisons. I'll probably get laughed at for referencing these shows, but hey, the comparisons work. Don't expect an out of the gate hit like Simon Cowell did!