Well the general gist of GW2 is that at every stage of the game you should be having fun. And leveling CAN be fun as long as you get a constant stream of rewards (like Alien Swarm) to play with. As for end-game content... who knows, they haven't revealed much yet, other than dungeons only being 5-man (which to be fair, is a good thing since they want to make it play as much like L4D as they do a traditional MMO). Hopefully there will be a lot of stuff to do, the end-game area (Which is almost certainly going to be Risen Orr from how the lore is going...) better have some fucking awesome events in the event system.

Also I read somewhere that each area has a level cap (e.g. the FIELDS OF BLOODY SMURFS Level 1-20). So that if you're say level 35, your stats and skills are leveled down to that of a level 20 as long as you're in that area, as a way of promoting balance and letting high level players help their low level friends without destroying the game balance completely.