I've been in good fun bands, I've been in good not so fun bands, and I've been in terrible not so fun bands for very, very short periods of time. Forgetting the terrible bands, what the difference was between the good fun and the good not fun was the attitude of the other musicians in the band. If you're playing with a bunch of talented jerks it's not likely to be any fun. I'd rather play with competent, but maybe not great musicians who keep a light hearted attitude in their approach to music. Let's use Michael Anthony of Van Halen as an example. Eddie Van Halen sounds like he was an intolerable boob despite the fact that the any version of VH with Anthony in it was a lot of fun to see and listen to. Now contrast that to the time he's spent with Sammy Hagar in Chickenfoot and The Circle, and he just looks like he's having a blast.
