I liked the original Kick Ass movie a lot. Sure, the protagonist and his friends are juvenile, but Hit Girl and Big Daddy are awesome, and the movie stuck pretty close to realism and most of the over-the-top moments were believable in the context of the movie.
In this sequel, well, we have high school drama, reality-breaking school bullies, a lower level of puerile, and, well, they kicked the wrong part of the original movie "up to eleven." Not only do we have wannabe villains acting like crazed and unrestrained two-dimensional gloating psychopaths (which makes sense), we have typical high schoolers doing the same? My suspension of disbelief is strained at that point, and then completely gets broken when, well, the response to bullying defies character, consideration of consequences, and scientific-biologic law. (Seriously, unless everyone involved in that scene were ALREADY in a bad way, that scene could not have happened.)
The only thing that prevented me rating this movie even lower was, well, even though it was a poor sequel it was still a sequel that reminded me of the original. And Hit Girl is still fun to watch as she kicks ass.