[raker]

Progression through Guild Wars rewards you with access to new skills. At any given time you can only bring 8 of those skills (and only 1 of them can be elite) with you at any given time. In addition, your character is limited to using skills from 2 classes. Many of the skills have specific interactions or triggers. Some skill specifically counter, defend against, or take advantage of other skills. Mobs have a set of skills (including some mob-only skills). The result is a logic puzzle that may have many solutions, left for the player to figure out.

Players have fairly easy access to all skills and max-level equipment in the game. Skills are (almost) never made obsolete by other skills, so you could very well be using the exact same skill you learned early in the game while you fight the final boss. The challenge is finding the combination of skills and gear to best suit your needs at any given task. Comparable to collecting tools to add to your toolbox, a screwdriver can solve new problems for you, but it doesn't make the hammer any less useful.

[digi_owl]

I have taken to liken GW1 to a trading card game.

You collect a bunch of cards (skills) and then build a deck (skill bar) from that.