Mate, you are missing out! Gamma World rocks. Although I do prefer some of the rules from the earlier versions to the current version (more mutations in the earlier versions, longer time period between Apocalypse and the game start, etc.) although 6th Ed does have a stack of cool stuff (nano, better handing of psionics, etc.).
If you need any more info, just drop me a line.
Cheers,
TGHO