I've never actually played any games on facebook, but I looked at the games list for about 3 seconds, and I'd say it's a pretty safe bet that 99%, if not all of them are horrible. Are there any decent ones at all, do you play any, etc?
The only one I played a lot was Assassin's Creed: Project Legacy. Its gameplay was basically a Mafia Wars clone, but it added a lot to the Assassin's Creed story, and also had a few unlocks for Brotherhood. Unfortunately, the studio behind it canceled the final mission pack, and instead released its story as a PDF file. :( I never play it anymore.
I've never played any Facebook games. I go on Facebook to keep in touch with friends, not try to manage a farm or whatever. Getting all those game notices spamming up my news feed is annoying in itself.
I used to play them a whole lot, but I don't play them anymore. They just got really boring after a while.