This. The game itself is awesome and I really like that there's an actual story while leveling up but there's just no endgame content. I've been playing this game for two months and I'm already fully equipped and I've seen every piece of the endgame except for raids because I don't really have time for those. And to make things worse even the hard mode dungeons are so EASY. The PVP content is nice and all but my comp isn't good enough to make it enjoyable so I've pretty much beaten this game and there's nothing left to do. I might pick it up again if it become free to play but I certainly won't pay for it anymore.
That said I won't pick up WoW again either. Diablo 3 and Guild Wars 2 are coming and they don't have cutsie little pandas.
MoP won't be as bad as it originally sounded. The pandarens don't look too childish. And you can't really hate on it when taurens have been running around in WoW forever. I like that they are focusing a lot on the fued between the Horde and Alliance. The talents are much different but they are actually shaping up nicely. The only really lame part is the companion battle system that looks straight out of a Pokemon game.
I have never played Guild Wars though. Not that I don't think I'd like it, I just never tried it out for whatever reason.