I too have played several MMO's: UO, DDO, and WoW to name the large ones.
UO was great for its time, and will always hold a peice of my heart, I still love the old theme music for that game
but seriously, EA needs to do something drastic to fix UO if they ever hope to revive it.
DDO was awesome for a pen and paper guy like me, NOT. Though it did not follow the pen and paper format, the game was a great game. It was terrible for solo content, but the elitiest like me found ways around that
The biggest problem with DDO was shear lack of content on release. I am the type of person that hates alts, but had 6 maxed out well geared out characters before I quit shortly before Giant's Hold was released. Had the game had more content, and not nerfed the hell out of my favorite class, I would have stayed with it. I miss it very much.
WoW though very cartoonish, after nearly 2 years of playing, I do not notice it at all. The game is the best I have encountered for solo content and has the best raiding system yet! The great many faucets that it covers is a stong selling point for me. Whether it be pvp, pve, raiding, questing, instances, socializing, rep grinding, or achievement grinding, there is aways something to do! I can not see me leaving WoW after the time invested into it. In my personal opinion, Blizzard is doing a fantastic job and keeping my free time occupied and entertained