Personally, I'm not a big fan of WoW. I never got past Beta testing the game. However, you can't argue the success of the game. It is the most successful subscription-based game in the world.
The non-subscription factor of GW2 is appealing and scary at the same time. I don't expect they will have any significant changes to the game outside of expansions that they can sell for more revenue.
From someone who played GW1 semi-hardcore (back in the day)...you won't run out of things to do...though the benefit of those things will be marginal. The original game did not push content quickly as the endgame content was quite a grind and quite difficult. Unfortunately the benefit of that grind was an armor set with the exact same armor values as every other piece of lvl 20 armor in the game...though it did look pretty freaking cool compared to all the rest. Stats in the original were determined by your character build and nothing else. Well one armor set might give +5 health, another would give +5 energy...BFD.
The original game was more about build and how good the player was...grinds were just for decoration. The pvp was fun, and I expect they'll do a good job with the new game's pvp as well...which has been lacking in mmo's for a long time now. The class interactions in the new game seem pretty amazing though...mage sets a fire, rangers shoot through the fire and arrows catch on fire and do extra dmg. I hope the mesmer has some kind of interaction...based on the original class I don't know how they'd do it...but it would rape just about anyone in pvp with the right build (or it could run away from the few builds that it couldn't rape).