I have been using the Marvel system, or FASERIP since i bought the original set back in 1984, have kinda home-brewed up the rules a bit by incorporating some things that i found in other systems and whatnot, but all in all it's worked for me and my players over the years.
I have never used straight Marvel characters, instead my best friend and i just created our own world and our own characters and just went hog wild over the years. We used the SAME world each time we played and it became one giant ongoing and long-running creation...characters/players came and went, characters died and/or changed their powers, skills, identities, and we made sure to keep track of what went on in our world so as to recap for any new people that came into our world to play.
It went smoothly for years...i mean decades, until around 2015 things came to ahead, the crisis' became more and more intense and i decided to restart the entire world/timeline over and create a new world with some hints and shadows of the world before so as to not start with a clear clean slate.
So now in 2020, my kids have grown up and have characters in this world and the last one, i have a stable group of players that are really invested in their characters and the world they live in and it's old school: we gather in my front room, grab pen and paper, roll our dice, and create magic!
My games are part RPG and part theater, we get into it, we have all become actors living out our superhero fantasies in the comfort of my living room....we don't dress up or anything like that (not that that's a bad thing mind you), but we really get to become our characters in our speech, our mannerisms, and our mindsets.
We have has some EPIC games over the years, we have cried when characters died, cheered when they are reborn, became angry when the villains won, and celebrated when the heroes came out on top.
I wouldn't trade any of the games we've played over the years for anything nor the players and their characters that were created.