I have thought about doing GW based on 3e or D20 Modern/Future, but the problem with Gamma World is that I think I just can't accept the conception anymore. The universe of Gamma World isn't a post nuclear war setting. It's needs to be a post trans-dimensional rift war setting, something like Half-Life but more gonzo. It's really hard for me to get past the magic now the way it wasn't when I was twelve or thirteen. I don't like the unrestrained magic. As much as I enjoyed it as a kid, it would be sillier now than doing a Thundercats RPG. There is just too much kitchen sink going on.