Unfortunately, Kick-Ass 2 is one of those films that proves the law of diminishing returns, which is why it was so savagely mauled by critics when it came out. Whether it deserved quite so much venom is up for debate, but it's certainly nowhere near as good as the original.
Some of the jokes - and the attempts to be as outrageous as possible - end up being a little tiresome and much of it feels like little more than a rehas of the original with less focus and too much going on. It wastes its best character in Hit Girl (and unwittingly killed her potential spin-off), replaces satire with silliness and vulgar attempts to shock for shocking's sake and the gloss is gone.
Given how badly underused Jim Carrey is too, it's no surprise he took one look at the final film and decided to pull his support for it.