Guild Wars is sort of like a graphically updated Americanized version of PSO, when it comes to how multiplayer is handled. It's pretty fun and best for those who ONLY play MMORPGs for combating monsters. It has no social or job system, in sight, which is why it pretty much mimicks the gaming-structure of PSO.
In a way, that structure almost perfectly explains why it is free. I've been mainly playing WoW, off and on, and GW. I may eventually get into FFXI, though. That whole Gill Farming is no different than just about every other MMORPG that has caught on to the same kind of shenanigans. It's like that whole fad where one idea comes out, and then EVERYBODY is doing it. So you either ignore it, or just forget about any MMORPGs right now. It's what you would call an exploit that's so generally unstoppable (under the legal actions you can do in these games), all you really need is the basic elements in a MMORPG to pull it off. It really depends on my mood, though. For some reason, I'm finding less time to commit to MMORPGs and have thought about sticking with just GW since it's free.
Guild Wars, like PSO before it, can technically be played by yourself or just with friends due to PSOs-like creating of world instances for all adventuring areas. It's overworlds and dungeons all to yourselves. (outside of the occasional little blurb about major Guild battles won, which determine what region of the world has access to special dungeons with extra goodies, and how far behind everybody else is from acheiving the privledge)