Ding 50!
Well I have played 99% of the MMO's out there dating back to Merdian 59, and I will have to say that WoW has the most polish of any of them.
The biggest problem that WoW did was make the leveling curve not steep enough, and are now dealing with end game issues. But then again I did the beta and have played scince launch, meaning that WoW is not my life, I play for a week or 2 get bored play other games and come back to it.
Any game that you play constantly for long periods of time is gonna burn you out. As for the people you never see log off the game, they are typically farmers or friends/roomates/college kids who share an account and use them as the Main to fetch items for the lowbies.
As for Guild Wars.... I can honestly say I really dislike it. And as Ray pointed out the interface and user friendlyness of it, is pretty shotty. I just recently just formatted my computer and highly doubt I'll reinstall Guild Wars.