I have yet to play the game, but here is a brief lowdown on rules. The basic combat and activation rules are the same as SBH, but there are some important differences in other areas.
Mutants and Deathray Guns is essentially the old Gamma World RPG translated into a miniatures game with campaign rules. Players can build a force of Pure Humans, Mutants, Animal/Plant mutants, zombie like canibals or Androids/Robots, or..... a combination of the different types. The characters are more template based than in SBH, for example all Pure Humans have the same basic profile. The rules provide for random skills, mutation and equipment rolls, which gives a nice scavengerish feel to your begining warband. Besides the basic Quality/Combat/Special Abilities profile as in SBH, MDRG has an upkeep cost for each character. This is used in the campaign rules to represent the logistics of keeping your warband alive between battles. For humans etc, this represents food but for robots it is energy cells etc. Most of the scenarios in the book reflect fighting over these resources, so it seems like it would make a neat campaign game.
David