While we often put these games under the heading of "Role Playing Game", they're really character advancement games. If that's what you enjoy, then perhaps Guild Wars will not give you the experience you're looking for.
After perhaps 40 hours, you can have a level 20 character. Your equipment should be pretty good, but obviously not "the best". You will not be able to get level 21, no matter how long you play.
So why do we do it then? Character advancement, for the player of Guild Wars, should be a means to an end, not an end in and of itself. If it is, the well will soon run dry.
We play because we enjoy the gameplay itself. There is no grind. There is no camping. There is no pointless wandering and waiting for groups just to "get some xp" which might easily be lost again.
There are missions. There are freeform zones to wander and explore. There is a storyline, and you can feel like you're part of it.
This isn't to say that there is no progress to be made after level 20. All of the content in the expansions will be geared towards level 20 characters. The gameplay dynamic is what's important here, not character advancement. What you will be able to do, however, as you continue to play is add more skills, play around with the skills and attributes that you already have, and recraft your character to your heart's content. If your group already has a healer, and you're a healer, you can leverage your other abilities, or change your skill-set entirely to more effectively use the different skills you've decided to pack. So you're not buying yourself "power", but flexability so you can synergystically leverage your enlarging set of skills.
IIRC, you should be able to change your secondary class once you've attained level 20 as well (though I'm not sure how this works).
In the end, it's important to "
Know Thyself".