As a guild wars fanatic I have been continually impressed with the character, environment, and monster art in Guild Wars - even moreso with Factions. A lot of the monsters you guys have worked so hard on are as fun to fight against ingame as they are to look at. Also, the character designs for the new continent and the two new professions is absolutely stellar. Even moreso when it's put to animation - the ritualist in particular.
Anyway I look forward to the next expansion, because I can't wait to see how the two new scythe-and-spear-wielding professions turn out. I saw some of the concept art on gamespot earlier this week and got really excited, so yeah - I can't wait!
Also as a side note, in the far future I'd love to see a "modern-day" power fantasy sci-fi themed setting for an online game using Guild Wars as a model. (I.E. the robust skill collection and customization + the highly detailed art style.)