Hmm. With so many less-than-shining reviews of GW I guess I'll weigh in. I love the game. It's the only MMO I've been able to really play. There are three reasons:
1. It's beautiful, obviously. I even have a crappy video card so can't play with the highest settings and am still impressed with the scenery, as well as the armor art for the various professions. The graphics in WOW completely turned me off to the game. I suppose I can appreciate that the characters all look like 80s action figures, but it breaks the feel of the game for me.
2. No fees. If I had been paying $10-$15/month for the past two years, I would not have stuck with it. Tempted as I am, I won't be playing Aion for this reason. Also, I haven't found a completely free MMORPG that's on the same level as the not-free ones.
3. I love the gameplay. I'm a big fan of the level cap (20) because it levels the playfield and gets you into the game fast. The player's the one who grows in experience, rather than your character. It also removes the need to grind. There's plenty of grinding to do, but none of it's necessary. The skill system, while totally saturated and offers too many choices, offers the same challenges that CCGs like Magic The Gathering do. You've got 8 people to a party, 8 skills each, so it's like building a 64-card deck. This allows room for straight-up strategic play or you can be creative and roleplay with your character. The challenge comes in building your skill bars for synergy and efficiency and then in actually using it, chaining skills, and managing energy.
/$0.02