Art. That's the crux of it for me. Superheroes are indeliby linked to comic books for me, and comics are almost completely about the artwork. Yeah, there are good comic writers, and some storylines are good, but really, when these writers write novels about superheroes, how many of them ever sell really, really well, in comparison to their four-color counterparts? Very few. So art is what draws me to superheroes in general. Most superhero games have just had shitty art. Sure, in the past both DC and Marvel had RPGs about their universes, but the art, while pretty good, was never that inspiring. Mutants & Masterminds had some fanastic art (first edition, but I'm warming to the art in the new edition), which continued in some of the supplements like Freedom City. I can't think of a superhero game that even comes close in the quality of its art.