Here is the link to an article celebrating TSR's Marvel Super Heroes released in the 80ies, and the homemade adventures that it inspired to the author of the piece!
Personally, even if I tried a ton of other superhero roleplaying game systems, I always come back to this one. It's simple and very flexible. 4 colors are not enough for you in the resolution table? Add more, I know a game master who did just that. As far as I'm concerned I added random damages and a variable resistance for protections. The system is very well suited to all modifications, without changing the core of the game. A masterpiece, I tell you... :)