The fact that they were un-augmented. The Spartan's are awesome and the only ones who can go mano-a-alien worth an elite or brute. But the ODST, and the rest of the military, are out ther mixing it up too. The drop pods are eye catching as well. When I first saw those things in H2, I immediately associated them with Starship Troopers, one of my favorite books. Finally, the fact that in the game their personalities were developed into real characters. The Master Chief was supposed to be the "faceless hero". He doesn't talk much, by design. In ODST we got to see the squad's faces, learn their personalities, see them struggle.