Themed characters aren't untraditional, but at least my group I think has found it much easier to find your unique theme in 4e than in some other systems. (Rolemaster can come close for casters, with its billions of spell lists, but not so much for non-casters.)
I'm quite happy with the superhero model for 4e: it fits with the gonzo-ness; it fits with the idea that physical conflict is a pre-eminent site of conflict; it fits with the team dynamics; it fits with the idea that your allegiances aren't just personal, but locate you within a particular social situation; and as GSHamster points out, it also fits with the approach to PC build.
Somewhat tangentially, the idea that super heroes have power levels that are at odds with traditional fantasy. I've just been reading The Conquering Sword of Conan (the 3rd volume in Patrice Louinet's critical edition of REH's Conan stories) and Conan is far more overpowered than most non-cosmic superheroes!