Sometimes, films (like all creative works) need to challenge the expectations of their audiences. To succeed, they need to do it well. One way to help facilitate this is to have done your homework, and the makers of Kick-Ass certainly did theirs. From the myriad well-placed references to comics and films that manage to rise well above the level of mere shout-out, to the considered construction of character and plot, there is ample evidence that this film's intention was to provoke its audiences to consider carefully our relationship with fiction, our position as active (or more likely passive) citizens, the nature of violence in entertainment and society, and also at least two entire genres; and it did so whilst enabling us to feel entertained - in terms of a slew of narrative elements - and more than a little disturbed.
Kick-Ass has received mixed reviews, due in no small part to so much of the violence in the film being carried out by an eleven year old girl. (In my humble opinion, the performance of that girl deserves an Oscar nomination.) This is understandable, and I won't begrudge folks who held this view. It IS disturbing. (If you don't believe me, read Lolita.) Often, great fiction is disturbing, for all the wrong AND all the right reasons. I think if you go into the film prepared to think, you'll find Kick-Ass a powerful, thought-provoking film. It helps if you like comic books, know your Tarantino and John Woo, have an idea who Buffy is and have seen The Professional (or Leon, to use its original title), but none of these are essential, I don't think. Well, perhaps they are; I mean, I know these things, and I'm sure it's helped me establish some pretty powerful contextual meaning. But I can't say that you won't be able to make other connections with differing material. (Napoleon Dynamite springs to mind.)
Kick-Ass is, I think, as subversively intelligent as Fight Club, made with a comparably audacious flair, but with just a little more heart, due in no small part to the wonderful performances from its young (and very young) leads. Go see it, but don't take your kids.
Seriously, don't take your kids.