NostalgicTortoise:
So I am asking potential players: What do you want from a game with super-powered player characters? Do you want something more like Amazing Spiderman #1, or something more like Alan Moore's Watchmen? Do you want to be John Constantine in Hellblazer, or the Punisher, or some other type of super? Are you open to hopping between different universes in a multiverse? Does your conscience get queasy if you have to cross a moral event horizon?
I would say that you'll get a thousand and one different answers to those questions, and very possibly different ones from the same people depending on the mood that they're in.
Different game styles and settings attract different players. You can run a game which is very 'Saturday morning cartoons' and you'll have players wanting to play very primary coloured heroes and villains, and I can remember having a fair bit of fun about a decade ago on here playing an X-Men Evolution game which rarely strayed beyond a bit of teenage angst and blasting things with energy beams.
Equally, if you run a very noir/morally grey game in the vein of a Punisher or Watchmen series, you'll get players who are interested in that and create dark, conflicted and messed up characters accordingly.
Most games probably fall somewhere in the middle because it's the ground where they're most likely to find a guaranteed player base. Within that, you'll get different focuses about where people want to play - some games will be combat focused, some will be more about the people behind the masks, a few will probably focus around shipping those people together.
I've not used M&M but I know it's seen as the standard 'go to' in the same way that 5e is (arguably) for fantasy dungeon crawling. I don't know how hackable it is to the extreme ends of the market, but if you're going for something down (for example) the Constantine side of things then it might be easier to pick a system which is much closer to the genre and just hack that - you can probably get 80-90% of the way to Hellraiser by using one of the WoD Hunter books and just moving some additional powers over from Mage, Geist or Vampire.
In terms of multiverses, some people will love them, some people will hate them - I'm not a fan, but other people will love the idea of mixing different realities and playing around with those dynamics.
In terms of moral event horizons, if you're going to do that then definitely advertise it at the start and be clear about what's going to be involved. If players are happy to be put in a situation where they potentially have to make that decision, then fair enough, but forcing a player into a situation where they have to make an impossible choice and then hanging it around their neck like a millstone without prior warning and consent is really not something I'd be comfortable with, especially as it potentially ruins that character for them without really giving them the choice.