Superman for the N64 from Titus has undergone some changes recently; it's developed something of a storyline over the last few months. In it, you have to rescue Lois and various friends as they are all being held by Lex Luthor. The old plot was basically fly around do good things. Titus has been working with DC Comics to get a better plot into the game - and to further develop gameplay while they were at it.
Right now, there are 14 levels, lots of superpowers (X-ray vision, flight, heat vision, and freezing breath), three skill levels, and two multiplayer modes.
We're hoping to catch a glimpse of the game next week. We'll update you on how it plays then.