I must admit that Guild Wars is here because of me. I'm the addict. Some say that Guild Wars pales before World of Warcraft. I don't care, it's my MMO, my social life ruiner

.
Why I play GW and not WoW? Two reasons. The first would be that it's free. Except the fact that you must buy the game, otherwise there is no monthly fee. You don't pay $15 for a game that you play like 2 hours/week.
The second is that it's not so "rushing". You don't have reasons to rush into this game. Reaching level 20 is easy, gathering skills it's easy and PvE is not such a hard job. The only thing where you are competing is PvP. Here is the big battle. Alliance Battles, Hero Battles, Guild vs. Guild are the only things that will put your skills to the test. Here you must prove you are better then the other.
In other words, GW is good for both casual player (including beginners) and hardcore players. I can't say the same thing about WoW.
If you have other opinions, please share.