From the introduction:
In 1984, TSR introduced a new Superhero RPG, using the licensed characters and world of the mighty Marvel Comics brand. Suddenly role-players found themselves able to have exciting adventures, taking on the roles of iconic heroes such as the Avengers and all of their members, as well as Spider-Man, Daredevil, and many others. The game was well-received, though it had its share of problems that needed to be “fixed” (aka, “houseruled”).
Mutants & Marvels is an attempt to capture the four-color awesomeness of the old, and infuse it with new, more streamlined mechanics, and present it in a more generic form. By using the OGL from WotC, it was possible to bring those aspects of the old game that gave it its unique flavor into this new iteration, thus recreating something familiar, yet unique. Of course, it’s up to you as players to determine how successful that effort was.