I just started playing GW2 a couple weeks ago and my first toon is still less than 40, so end game is far away for me.
However, the feeling I get is that it will be a long, long time before I get bored. I'm a completionist type player- I have a very hard time leaving a zone until I've collected every heart, skill point, vista, POI, and as many of the events as I can find. I also farm everything, explore everywhere, and do all the jumping puzzles to nowhere just because I can. And GW2 rewards that kind of behavior. I ran into a random corner in LA last night and ended up doing Weyndat's Revenge, which is one of the best open world exploration experiences I've had anywhere.
I've hopped into WvW a couple times, but I stay away from the fighting and grab as much exploration stuff as I can. I've never been big into PvP. That may cause me some issues down the road, but for now I'm not worried.
I will definitely level my huntsman and leatherworking to 400 and craft at least one epic. I'd like to level other professions and craft epic components and high end gear for guildmates too. And then I'll do cooking, just because I can.
It does concern me when I hear that the PvE boss fights are shallow. I loved the strategy of WoW raids (vanilla Ony and Naxx among the best) and I would like to see that in GW2, even for 5 man groups. Especially for 5 man groups. Getting even 10 people together can be a headache, let alone 25 or *shudder* 40. Even so, I plan to hit dungeon explorables hard, and if they are too easy, I might have to come up with ways to spice them up.
Not only that, but having a solid guild to lean on is going to make a huge difference. There's always some one who needs something, is leveling an alt, or wants to run naked thru CM. I'll be there for those people, and it will be a lot of fun.
