Also a serious contender for Best Selling Supers RPG here in 2025, and back when d20 games were all the rage its only serious competition was 5th ed Champions/HERO - and that despite it feeling like a awkward fit, as noted. 3rd ed has been out for quite a while, and there’s a new licensed release based on Valiant Comics that sounds like de facto preview of what might appear in a 3.5 or 4th edition.
M&M almost always shows up in recommendations for a supers game system when someone asks what they should use, although often with a weirdly apologetic tone (“This may be too crunchy for you, but…”) these days. There are solid lighter systems out there - I’d rate the SCRPG as one of them as well things like Supers RED, Prowlers & Paragons and BASH just to name a few - and the last three editions of Champions/HERO all offer slighter crunchier rules for those looking for them. But outside of certain niches (Masks with its “coming of age” drama-fest, for ex) M&M is about as good an option as any for handling supers tropes in an RPG, and much better than some.
Also has a ton of supplemental support, more than anything but Champions, the old TSR Marvel game and its legion of modern FASERIP-inspired retroclones, and (weirdly) Villains & Vigilantes, which has a crazy number of adventures and villain books without doing something I’d call a setting/city book.