Full disclosure: I learnt to play D&D with 3.5, and I played it to death. My group at the time tried out 4th Edition when it came out, we gave it a fair chance.
Overall, we didn’t like it.
So when my new group suggested playing Gamma World, a setting for 4th Edition, I was sceptical at best.
When CERN turned on the Large Hadron Collider, all possible universes collapsed into one, resulting in a Weird Shit apocalypse. That was 150 years ago, and Weird Shit is still going on in this post-apocalyptic world.
You play a character who is the result of two possible versions of yourself being mashed together.
“Which two?” I hear you cry.
You randomly generate them. In our current group we have a telepathic birdman, a demonic plastic toy, and a pyrokinetic nightmarish horror. It’s a weird game.
Playing The Game
Being a setting for 4th Edition, the rules are pretty much identical, with an added layer on top.
This layer is called “alpha powers” and is represented by a deck of special cards.
The setting goes that the universes are still shifting in and out of each other, so that at any one time in addition to your base two power sets you also start with one of a huge range of other powers.
They range from having clown feet (+10 swim speed) to being able to teleport at will, to having a third arm. They are what makes the whole game utter chaos and a hell of a lot of fun.
There is a lot more to the setting than I have touched on here, including the disposability of characters and the fantastic rulebooks that nail the level of humour.
In conclusion: This setting is perfect for a one-shot, and I would definitely recommend giving it a go if you get a chance. Special mention also goes to The Pathology Guy for this fantastic automatic character generator http://www.pathguy.com/gammawor.htm.