If you do not play GW2, please do not bother responding, this thread is for people who actually enjoy and play GW2.
I wanted to throw out the question of whether the CURRENT players think this game has longevity for them - PvE wise, WvW wise and in sPvP.
Personally I'm levelling my third character to 80 - a mesmer this time around. I'm having as much of a blast doing it as my first 2 characters, warrior and guardian. I tried, but did not enjoy playing elementalist. PvE wise, I don't think it has longevity for me - there is a lack of "real reward" after 80 and obtaining exotics, which is not a large task. I have 100% completion on one character and it's pretty unlikely I will go through that again on a 2nd. Legendary doesn't count as "a carrot" because it's a MASSIVE time investment for a small reward. It's a catch-22 though, because this is one of the things that really attracted me to GW2 (no grinding at 80).
However, I think this game will entertain me for a long time to come because of the PvP, I think it has a lot of depth and I haven't even scratched the surface of what I want to learn. I play for about 6 hours a night and I usually log off reluctantly already thinking about what I'm going to do in it the next day/week/month.
So I say: Yes, it has longevity for me. I can see myself playing this game for a long time, especially with the regular content updates.