I also want to put in a good word for 4CtF. First, I have to say that I prefer Mutants and Masterminds for a "standard" superhero game; it drops the parts of the D20 rules set that I personally find incompatible with superhero gaming -- AC, hit points, classes, levels, etc. What I find so appealing about 4CtF, though, is that it provides a mechanism for filling one of the gaping holes in the D&D system.
To elaborate: heroes in myths, legends, novels, films, etc. often have unusual abiliites or high levels of competence that are impossible to represent with standard D&D rules. That role in D&D is instead filled by magic items -- heroes in D&D are more often defined by the things they have rather than what they can do. This is one of the reasons that "low-magic" games so often fail; without many magic items, the characters will never be able to approach even the abilities of action-movie heroes, much less ones from high fantasy.
4CtF provides a way to substitute innate abilities for the assumed level of wealth & magic items from the DMG -- whether special powers, enhanced stats, or additional skills and feats. It's a nice alternative for DMs like me who are tired of D&D's heavy emphasis on equipment, but who still want to run heroic games. In fact, using 4CtF allows me to much better simulate characters from fantasy and film that the "standard" item-heavy D&D approach.