I have played wow on and off since beta. I've played some single person computer games too far more compulsive like Dragon Age Origins/Awakening.
I return to WoW because it's familiar "evil" and honestly because it's such a theme-park and has colorful cartoonish graphics.
I tried Conan, but it was way too heavy to run properly (fixed that but too little too late), beginning area was much better than rest of games, and it was inbalanced, had broken stuff and was realesed unfishished. Lesson here, unfinished realeases are bad.
I tried warhammer, it was kinda unfinished too, and not as cool as it seemed while making. It was different had more pvp focus, I might have played it more if not for beging also released unfisished (though not as badly as conan) and they really had bad log-in server and really bad customer service for european accounts. And then there was merge of accounts into american servers. I wasn't playing at the time and when I tried to come back I found out my accout information was broken. My account was operational but I just coudn't log into game. And turn out this ownership of accout became so complicated (?) that it could not be solved by e-mail/fax and I would have to call their customer service in US. From Finland yeh right, that would cost more than new game, bye, bye, Warhammer. Lesson here make sure your customer service and servers can handle international customers.
I tried Rift too. I hadn't played WoW for year and rift had been out for couple of months. I didn't like it becuase I didn't like graphics, they were pretty but too gloomy and general dark colors made spotting some quest objects hard. Also I liked rifts in Rift. But they had some constant seasonal stuff going on that caused only 2 element rits to appear and none of the other. So you coudn't do certain quests. Plus it was bit more buggy than WoW. And talent system was way too complicated. Hard to get what is good without doing extensive research out of the game. And noob don't want to do that. Plus leveling was really slow, and single plying harder since fights were harder compared to wow minus Cataclysm mob boost. Of course in WoW you hit that by 80 plenty of time to learn to play your class.
I probably end up playing whatever new project blizzard is coming up with, because they don't release unfinished games and I kinda trust them, that whatever is coming is at least playable maybe even fun. I think I am eternal WoW returnee since there are no viable obtions.
I probably try 40 000 warhammer too when/if it comes.
And y, I think I try that Golarion game too.
I tried FF online too, but it's grindy as hell, no thanks.
I haven't played Eve, but it has it's fans. So apperantly good enough for it's niche.
New Star Wars universe game is going to be big seller. Still my WoW friends got that blizzard's offer for year of wow and free diablo III (smart move form Blizzard), just in case it would suck. Thay pre-ordered that long ago, as they desperately want to find something good to play that is not like WoW.
And btw in MMO it's very rare to find actual (constant) roleplaying happening even at so called RPG-servers. Grind/Instance/Raid stuff kinda kills it, not just for "tactic" things, but because they are repeated ad-infinitum. Sure some guilds have some roleplaying going on but it only semi-interracts with the game. MMO is not rpg-friedly enviroment unless paizo devises some quite new approach. And problem with new is that it doesn't always work.
I would be interested in Golarion MMO. Bacuse Golarion universe makes potentially interesting backdrop for such game. So if I will actually see one in future I will try it out. Prolly just for one month, unless it's actually fun/playable.