I think the primary problem with superman is the setting. There are very few people on the DC earth who would pose a threat. I mean there might be Specter, Manchester Black, Black Adam (maybe) and that dude with the ability to both copy powers and increase them (Paradigm? Paragon? I forget his name, but he was a villain but helped superman fight the giant daxamite robot thing) but for the most part most of the enemies superman is a match for are not on earth.
Now, if they did a game in outer space, or with lots of alien enemies, THAT might have potential. Perhaps if they made a game based on the Miniseries "invasion" where a whole bunch of different alien races team up to take Earth down, we might have an exiting game.
Still, I think there are plenty of DC universe characters who would lend themselves better to a video game than superman. Admittedly, most aren't exactly top tier, but I would love to see games based around characters such as Green Arrow, Flash, the JSA, Blue Beetle (either Ted Kord or Jamie Reyes), maybe even Booster Gold.