I think peoples mileage vary on this one. Depends on phone & what you're updating to, & when. On Eclair (blur rom) I got lock screen freeze so updated to (leaked) Froyo, which was very stable but bland. Up to CM7 & I like all the extras built in, OK a few very minor cosmetic bugs in there but nothing to make me back step. I quite like it's improvements over Froyo, & if using a different launcher & the same apps as before I don't notice much difference, until I go into menus.
I guess I could try more up to date nightlies, but can't be bothered. I'll keep reading the CM10 threads until I'm satisfied the significant bugs are gone.
I read someone thinks that Jelly Bean is too much for some earlier phones, like mine. I think someone even suggested staying on CM7 (obviously for you guys, GB is bad, so....).