I don't often get the chance to say this, but sometimes you need to bench the writers and open up the jumbo can of stupid. Stupid is not usually in short supply, either in Hollywood or real life, so I rarely find myself thinking that there isn't enough of it directly in front of me.
It was only when I was most of the way through Kick-Ass 2 that I realised how important stupid had been to Kick-Ass. Action movies need to be stupid. Partly it's down to the fact that no-one's going to an action movie for a healthy dose of reality, but mainly it's because most of what's happening in action movies is just plain wrong, and you need some stupid to take the sting out of it. If you stopped to think about the collateral damage of the average outbreak of hi-jinks (as some people have about Man of Steel, the climax of which involved more property damage and loss of life than every major incident which has ever happened in real life in the USA, all put together), you'd get all shaky and upset, so it needs to be somewhat ridiculous so that you can take a long calming breath and remember it's all a movie.
What lifted Kick-Ass above mere stupidity was the electric presence of Chloe Moretz as a tiny foulmouthed hurricane of violence, and she's also more or less the only thing which saves Kick-Ass 2 from falling flat on its face. But even Hit Girl doesn't quite work any more; what was shocking and hilarious because a pre-teen was doing it is somehow just worrying when a teenager is doing it. Take away what one little island of cartoonishness and the whole Kick-Ass thesis becomes a rather dreary meditation on the consequences of vigilantism.
Slightly notoriously, Jim Carrey had second thoughts about the movie and refused to do any promotion for it on the grounds that it was too violent, and he wasn't comfortable with it. I'm not sure how those concerns didn't bubble to the surface when he read the script and presumably watched the first movie to see what it was about. But we all have these moments of clarity after the fact - I'm waiting with interest to see his moment of clarity on MMR vaccination, for example. Thing is, I think he's just wrong. Both Kick-Ass movies are hysterically violent, but the second one in particular goes out of its way to make violence not cool. What may be driving Jim Carrey's second thoughts is that his own character revels in violence quite gleefully, and that gets punched up in all the trailers. What doesn't get covered in the trailers is that Col. Stars and Stripes is a more rounded character than that, and when he gets killed horribly it packs a meaningful punch. That isn't true of the dozens of mooks and non-speaking part cops who get arbitrarily wasted in an effort to let us see how horrible the super villains are, but the character deaths carry weight.
Of course, it all depends on what you want to read into it. The superheroes are mostly a bunch of self-deluding inadequates, the super villains are creeps, and almost everyone in Mindy (Hit Girl)'s high school is toxic. There are a couple of reasonable moderate decent guys, acting as various kinds of father figures and they have an impressively high casualty rate. Across the two movies, every single father figure gets straight up murdered, usually pretty horribly. Throw in Wanted and it all gets downright worrying. I can't imagine Mark Millar's actual message is that being a father is suicidal, but if I was his dad, and had somehow lived to have the conversation, I'd be sitting down with him and saying "Son, is there something we need to talk about?"
It's popular wisdom that smart people avoid movies with a number in the title. Kick-Ass 2 isn't a terrible movie; standing on its own, it's possibly even not a bad movie, since it's got a plot and characters and character development and an actual message (it's also got the best idea I ever saw for sub-titles - speech balloons!). But it's not a fun movie. There's a load of trailers up on the internet and if all you want is the fun you had at the first movie, you could pretty much catch all the best action beats in the trailers - including both of Hit Girl's best action scenes. Or you could just watch the first movie again.