When I went to see Megamind, I knew exactly what I was getting into. I research movies before I see them, and so (because of spoiler-laden trailers) I could guess parts of the movie before they happened. I've told everyone I know and now I'll tell you: Megamind is really amazing. I want to own it, I have thirty fanfics for it, I'm a geek for it, and I saw the movie THREE MONTHS AGO. Usually my geek-out phases only last a month or so.
Now, I understand the arguments against it. Some people don't like the animation, or that it's animated at all; some people say it's not original enough; I've heard complaints about the songs used, the fact that it is clearly a Dreamworks production, that it's predictable, that it's a take-off of countless other things (mostly of Superman/Despicable Me), that they don't like the voice actors or the childishness, or that it was, of all things, boring.
If you don't like animated movies, the first thing I ask is "why", but that's your issue to work out. If you don't like the style, once again, your issue, as there were no clear flaws that would disturb the standard audience.
If it's not original enough/a take-off, the movie is aware of this: it is knowingly parodying all the other superhero movies we've seen in its concept, as well as subverting and deconstructing several of their associated tropes, and it does a thorough job of it too.
If you don't like the music, it's a taste thing: I'm sure a few people in Metrocity didn't like "Highway to Hell" either.
If you think it's childish . . . I dunno what to say. It could have been much more immature. I personally found the immaturity present to be at a realistic level.
If you don't like the voice actors, again, why? Everyone did a good job, and if a voice annoys you, once again, it's personal taste.
If you were bored, I'd like to know why. No one ever gives me a reason. Tell me why and we can reason together.
Finally, the accusation that "it's just another Dreamworks movie." I'm so sick of hearing that. Yeah, Pixar's great, but it's not GOD, and other animation studios should be given a chance, especially when they put out fabulous stuff.
For all the things you can fault it for, Megamind has solid plotting, characters, a fun premise, and a spirit I adore. Check it out!