Scott Renshaw at Letterboxd says it succinctly:

If your movie encourages the audience to consider it a whoop-it-up, did-you-just-see-that moment when a villain kills two police officers with a lawn mower, you’ve set up shop squarely in Morallyreprehensibletown, and thanks but I’ll keep driving.

Matt Singer at Letterboxd agrees:

This movie takes the biggest problem with the first film, its uncertain tone, and amplifies it. The whole gag of these KICK-ASS movies and comics is supposed to be super heroes in “the real world.” “This isn’t a comic book, this is real life!” characters in KICK-ASS 2 say on multiple occasions. But Mark Millar and Jeff Wadlow cannot resist an opportunity for a puerile gag or outrageous stunt. This is a movie where a character pukes and poops simultaneously — “in the real world!” One scene might have a gag about a dead shark (a pretty funny one, actually) and the next might see a major character brutally murdered. Then there’s a poignant funeral, and then a gun battle full of wisecracks. It’s a total mess.

Ali Arikan at warns us:

… for those with horrid taste in cinema, questionable politics, and terribly short attention spans, i.e. the target audience of this movie, I feel it is my duty to say: Don’t see this film. Do something else. Enjoy the final days of the summer. Solve a crossword puzzle. Call grandma. Do whatever you like. But don’t see this reprehensible movie.

Tasha Robinson at The Dissolve wastes no time detailing the film’s ugliness:

At one point in Kick-Ass 2, the antagonist sets out to prove his dominance over a specific superhero by raping the guy’s lover. As one of his minions holds the struggling woman, he gloats over her helplessness and tells her she’s done banging heroes, and she’s about to experience “evil dick” instead. Then he can’t get an erection. As she mocks him, he turns away and desperately tries to stimulate his uncooperative penis; finally, he whines that he’s just not in the mood right now. … [T]hen, the villain tells his minion to viciously beat the girl instead. She winds up hospitalized; meanwhile, another minion murders the cops who arrive to rescue her.

This sequence is Kick-Ass 2 in a nutshell: a messy, confused, over-the-top mixture of brutality and sick comedy, puckishness and ugliness, self-awareness and tone-deafness.

She continues, comparing it to its comic-book source material:

In the comic, the villain does rape his victim, and there’s nothing satirical or smart about it. The protagonists are visibly much younger; John Romita, Jr. draws them with such skinny limbs and big heads that they look like toddlers. And the comic is relentlessly bloody, with a high body count including children and animals. (In the comic, The Motherfucker decapitates an enemy’s dog; in the film, he gasps when someone suggests it, and says he isn’t that evil.) The same thing happened with Millar’s comics seriesWanted, which was also adapted into a film, and also considerably softened, especially in its depiction of rape. The comic is simply about brutality; the film is about trying to make that brutality funny, and about making it safer for audiences in the process, but that often just makes it seem petty.