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 😉