I personally love MMO's and I've tried ALOT of them...good and bad. I'm a confessed addict to WoW, and I've gotten my brother and nephews addicted as well, but there's alot of interesting MMOs out there. I currently have a lifetime membership to LOTRO, even though I don't play it, but I am looking to get into Eve again, when the new big patch hits to allow you out of your ship. Overall, like FPS or RTS, MMOs have their pluses and minuses, and it looks like WoW is the one to beat for the foreseeable future:
http://news.bbc.co.uk/2/hi/technology/7960785.stm








