Imagine Wile. E. Coyote finally caught the Roadrunner. Imagine Lex Luthor (really) defeated Superman. Imagine Bluto kicking Popeye's butt for good. That's the type of story Megamind wants you to see.
Super-villain Megamind (voiced by Will Ferrell) finally beats his archnemesis Metro Man (voiced by Brad Pitt) and has Metro City at his clutches. But he soon finds out that life as a supervillain is meaningless without an archenemy. We eventually see that Megamind is a good sould in a monster's body and is willing to be the good guy. (Hey, didn't we see that in Despicable Me?)
Over-all, the film's concept is derivative of the aforementioned Despicable Me and The Incredibles, which could have been great, except that the film lost a lot of the heart in the derivation. The movie does have funny bits to offer, but gives marginal enjoyment in my opinion. The animation is superb though.
Megamind is an OK family feature and will be easily forgotten once the next animated movie come.