gw1 is famous for the fact that you haven't had your build complete when you got to max level
gw2 isn't different:
-) you won't have all the heal-, utility- and eliteskills when you reach max. level. Quote: "The healing, utility, and elite skills (seen below) are now unlocked with skill points. Skill points can be acquired by undertaking what we call a skill challenge. There are 200 skill challenges in the game, and they range from defeating tough opponents, to answering riddles, to drinking a particularly potent drink.
-) same thing with traits: traits are modifiers for the skills you use, they change them in a small or big way. AoEs can become single target hitters or a shadowstep can cripple your foe. These traits will be there for you to find them too, even long after you reached max. level.
So 2 big points how you can progress after hitting the lv80 mark. Don't know why no one mentioned it yet. Its a way to develop your build to your liking; I think Blizzard wanted to do this with the Path of Titans before they scrapped it...