The game delivers, period. It has set the standard for a new age of MMORPG's.
The combat system feels natural, and you get experience for just about everything you do in the game. It does have a main quest line to follow, but they only occur every few levels. I really feel like this game was tailored to keep it fair for casual gamers that don't have endless amounts of time to play every week.
The other thing I love is that you will not ever roll over any opponents due to the fact that your character's level will scale downward if you are in a lower level area. They thought of so many aspects of the game, and overall GW2 is just a joy to play.