errr.... Dave's a meglomaniac and doesn't work well with others.
Megadeth was great up until Peace Sells. Once Chris (I forgot his last name at the moment) left they lost their sound. All those killer solos on Peace Sells were his work and that album is what put Megadeth over the top. If Dave Mustaine's ego would just take a vacation I bet things would improve as far as the music coming from Megadeth lately.