5 votes for Runescape, while I'm the only one who voted Guild Wars? Blasphemy. I understand WoW being in front. Even if I sincerely dislike WoW, I can see and understand why people enjoy it so much.
Here's why I love Guild Wars:
1) The community. Even if you have your standard fare of MMO idiots and jerks, the "good" players really shine. They're helpful, friendly, fun to play with, know the game inside out and are very generous.
2) If I don't feel like grouping, I'd get my henchmen to help me out, or even better, my Heroes.
3) The art style is very unique, and the graphics have aged very well. Also, the best armor designs I've ever seen in an MMO.
4) The world feels alive. As someone who has Master'd several tabletop games, this game uses all the right techniques for making the world seem alive. Small, petty conflicts between factions (for instance, the merchants and the bankers), NPC's with personalities (GASP!), Cooperative Missions are amazing to play, especially with a good group.
5) This one I'll never tire of repeating: Skill. This games doesn't reward time spent playing, it rewards pure Skill, strategy, teamwork, and understanding the mechanics of the game. Also, PvP is well organized, with frequent tournaments, LOTS of modes. All WoW fans saying WoW's PvP is better can go suck it play Guild Wars.
6) Instanced play. Some people hate it, I personally love it. It's a more self-contained experience: just you and your group kicking ass.
7) Vanity. No game puts a greater focus on your own vanity and ego. I don't care if you're the best player in the world, if you don't have a rare minipet, special armour and look absolutely stunning in your armour, it's all for nothing.