I recently attended PAX East with a few of my friends. While attending a panel, my friend Shawn was lucky enough to win a free copy of Gamma World. Long story short, instead of playing some Dungeons & Dragons Encounters at some tables that were set up, we opted to break open the game and have Lance and I play around in the set.
It was fun.
The game is zany as Hell, and also a bit rules light. There are a lot of 4th Edition staples in the game. The power system, defenses rather than saving throws, hit points based on Constitution score (rather than the Constitution modifier), and so on. The skills are further stripped down from 4th Edition, obviously you don't need stuff like Arcana and Dungeoneering in a world that does not include magic and dungeons full of aberrations, although a lot of Gamma World enemies could definitely double as 4th Edition aberrations, there is a Dogdamn land squid for Pete's sake.
There is also a land shark. It, like the bulette, makes me oh so happy inside.
The setting is pretty broad, some time ago, something happened, possibly science related (I vaguely recall reading somewhere that a super collider was involved), and mashed all the alternate futures and timelines and eras of the universe into one ball of madness on earth. It was then dubbed Gamma Terra or Gamma Earth, and chaos very quickly followed.
Your origins are your key feature, they determine whether you are just a mutant human, a hawk man, a swarm of rats, or a giant cyborg cockroach. I was a Doppelganger Felinoid called Lyano, I could use cat claws and summon alternate selves of myself. Lance was an Android Pyschic, he could grab stuff really hard and use mind bullets and whatnot. Anyway, your origins (you roll for two, a primary and secondary), determine two of your scores, which type of mutation you have affinity for (Dark, Psychic, or Biological), and also what skills you may have a bonus for. They also determine your powers and critical abilities. This isn't like 4th Edition where you have a shit ton of options for powers, you get an at-will or encounter power for each origin and a few others as you level, you never have more than a few, even at level ten, which is the level cap at the moment.
The equipment section is pretty much my favorite part of the rules (excluding crazy origin combinations), you have a lot of leeway in that area. There aren't like fifteen different types of armor, just three. Light, heavy, and shield. It is left up to the player to determine how that armor looks. Is your heavy armor composed of a 55' Chevy Bel Air hood and road signs? Or is it thick slabs of tire rubber bolted together and tied to you with chains? The weapons are just as simple: heavy and light attacks, heavy and light melee weapons (like a signpost or a knife), heavy and light guns (like a .22 or a .45), and heavy and light ranged weapons. (a thrown bowling ball or a thrown knife). Light and and ranged stuff tends to use Dexterity, while heavy stuff tends to use Strength. Pretty straightforward and intuitive, and again, it is up to you to determine your weapon or attack's nature.
Your starting equipment is randomly rolled, as is your skill bonus. You roll a die, which determines how many times you may roll on a very broad table. You can end up with things like fuel, toy cars, boats, horses, or laptops. Or trucks. The table doesn't go to deeply into what stuff does, other than miles per gallon and passenger capacity for trucks and "you'll figure out what it can do" for everything else. Lance and I had two horses and a boat and some generators. We probably should have tried to make some kind of cyborg boat horse generator that shot lasers. Next time.
I said before that the skills are pretty light. You get stuff like Mechanics, Conspiracy, Stealth, Interaction, etc. Your origins determine your bonus in two skills, and you roll for a random bonus to a third. The equivalent would be being trained in a skill in 4th Edition. There are only a few skills and it is pretty easy to figure out what they do.
You also roll randomly in stats. Your origins determine your ability scores to a certain extent. Each origin has a ability associated with it, Dexterity for Felinoids, Intelligence for Doppelgangers, and so on. Your primary origin ability stat is 18, your secondary is 16. If both origins have the same, it is a 20. Everything else is 3d6, no rerolls, in order, do not add anything. I rolled a 7 for Strength and a 5 for Constitution, which isn't as bad as it would be in other versions of the game. All the powers and stuff are like 4th Edition and you can use Intelligence and Wisdom and non-Strength scores and such to make attacks.
Gamma World also has guns and I really like the rules. Guns fire ammo, Gamma World doesn't get into energy cells or bullets, you either have ammo or you don't. You have two options: conserve ammo, or spray and pray. If you are conserving ammo, you may only fire a gun once an encounter, but you'll still have ammo at the end of the encounter. If you are not conserving ammo, you can fire your gun as many times as you want during an encounter, but you are out of ammunition at the end of the encounter and will have to find or barter for more afterwards before you can use your gun again. I like it, it is pretty simple and easy to manage. I gave up tracking ammo a long time ago in my Hekinoe
I want to take a moment to mention that you have a lot of leeway to just decide things in the game. It is a really cool feature. If you get the Hawkoid and Seismic origins (and this is pointed out in the books), it doesn't mean you have to be some weird earth eagle man from underground, though you can be. You can say you're a gargoyle if you want. If I had wanted to, I could have said that my double from the game we played was one of my Felinoid's eight extra lives that could pop back in time to help me out. ...That is actually a neat idea, I regret not coming up with it then. Oh well. There is a lot of free reign in this game and that is an awesome feature, and only adds to the zaniness I spoke of earlier.
Zaniness. Even in the earliest incarnation of the game (back when Gygax and his son worked on it), the game was not super serious. It was about mutants and lasers and bat crap crazy radiation induced mutations from alternate dimensions mish mashed with this one cause all manner of shenanigans. Lance and I fought badger and pig men and giant lion bat things by shooting lasers, throwing bowling balls, summoning alternate selves of myself, and using a blow up doll.
Is it any wonder that Shawn TPKed us? Is it any wonder that we were laughing and giggling and having a super fun time?
Alpha Mutations and Omega Technology. This is a button issue for me. Every encounter, you have random mutations that can affect your character, in addition, you can draw Omega Tech cards after some abilities. These are loot basically. For instance, my Felinoid had a mutation affect it called Stink Glands and Lance had a tech card that was like a Fusion Rifle or something. The mutation cards can be overcharged for an additional effect, you make a d20 roll and add a bonus to it if you have one (some origins gain a bonus to certain overcharge rolls). For instance, Stink Glands gains the ability to do poison damage in addition to its other effects. If you fail overcharge rolls, the mutation goes haywire and you end up with a penalty of some kind (-2 to attack rolls for Stink Glands). Omega Tech doesn't operate the same way, but there is a chance you could deplete an item's charge and end up with a broken Fusion Rifle or Freeze Ray, you can still use the item, but it is very much less effective.
Now, the button part of the issue, you can buy booster packs for these mutation cards and technology cards. No. We are already letting Magic: The Gathering get way too involved in 4th Edition with all these power cards people are bringing to the game and the Harrow Deck or whatever it is being sold now. I played Magic, Pokemon, and the World of Warcraft card games. I love Munchkin. I dig games and card games. I do not dig Dungeons and Dragons, or even a variation of it, having a collectible card game as a main component of it, especially not when you consider the amount of power creep that occurs between sets of Magic: The Gathering. Lance and Shawn have advised me to just not buy boosters packs and just use the cards out of the deck. I can live with that, but I still don't like this trend.
There are no feats, or classes, or even that many levels. It is essentially a stripped down version of 4th Edition, but what it loses isn't that important. There is a lot of flavor packed into the game where the rules were removed, and I like it. I tend to favor complexity over simplicity in most games, but Gamma World's flavor is robust enough that I have a rollicking good time playing it.
So yeah, if you want some crazy fun and think the 4th Edition ruleset is a solid ruleset, Gamma World might possibly be for you.