While there had been R-Rated comic book movies before Deadpool's release a couple of years ago, there weren't any that changed the game quite the way the Merc With A Mask's debut (let's ignore Origins, eh?) did. It was such a success that it has led to a serious conversation about Marvel making R-Rated movies again, which is a huge swerve for the company, given the mostly family-oriented material of the MCU.
And now that they've basically got Deadpool back from Fox (assuming the deal goes through), there's a good chance that that consideration will have to become a reality. Because there's no way Disney's shareholders would be dumb enough to kill off a lucrative brand (or worse, sanitise it for a PG-13 rating). It's an odd prospect, but it's not like R-Rated superhero movies are unprecedented, even by Marvel. And if they're smart enough to keep Ryan Reynolds as the creative drive behind it, there's no reason why a Deadpool MCU movie couldn't work. Just go with a multiverse explanation and we're cooking on gas.
The problem that Disney might struggle with more is that there haven't been that many genuinely GREAT R-Rated comic book movies, and Marvel's overall record has been... patchy at best. There are lessons to learn in there, for certain.
So how does Deadpool rank alongside the 12 other R-Rated Marvel (and Marvel imprint) comic book movies?
The big screen adaptation of Man-Thing is so terrible that it should come as no surprise that most people have simply forgotten it exists. But it should come as a surprise because of when it came out.
Released at the zenith of Marvel's first boom period for movies in 2005, with two X-Men and Spider-Man movies already out, it was a dull mess whose sloppiness is utterly confusing.
It was made by The Lawnmower Man's Brett Leonard, whose affection for the computer "wizardry" behind that movie was such that he simply ignored the need to update it at all, horribly dating Man-Thing immediately. Added to that a fundamental misunderstanding of the material and it's no surprise that it didn't even get a US theatrical release.