Unlike Dungeons & Dragons (and most role-playing games that I've played), Gamma World encourages you almost completely randomly generate your character with the exception of a few power choices made throughout the course of your career. From a table of twenty origins you roll twice, and these form the foundation of your character concept (and if that's not enough, the next expansion will add twenty more). If you want more control, the book recommends rolling for either your primary or secondary origins, picking the other, but if you really want you can just pick both. On one hand, I like the challenge of being forced to merge to random elements together, but on the other I just want to play an adorable swarm of kittens (or ferrets) linked by a hive-mind.
Your origins determine the one-or-two key stats that you'll be using to blast, tear, and mind-rape victims apart as you tour the wastes: the primary gets an 18, the secondary a 16, and if both use the same then its a 20. For the rest, you *GASP* roll 3d6...in order. I fucking hated rolling stats in the past because commonly I had a concept in mind, and rolling--especially in order--was a surefire way to fuck me out of a good time. This? Not so bad. I could see doing this in D&D games, having characters roll stats but nudging their keys up to 16 and secondaries to 14 if they roll less than that (before applying racial mods). This would virtually guarantee functionality, but I digress.
Once you've determined your origins, you get all the traits--with the exception of the level 2/6 critical ability--and novice powers, which serve as your at-will attacks. All origins have a utility and expert power, from which you can choose from either as you level up, ultimately getting both. While only six powers over the course of ten levels it might not seem like a lot, but you get access to continually fluxing mutations and technological doodads that are determined by drawing cards.
Before I go any further, some people are pissed that Wizards has added a random, arguably collectible element to the game. The game comes with an ass-load of cards, more than enough to play by itself, but if you want you can buy additional boosters. Again, the game comes with everything needed. You don't need to buy boosters. It's not some fucking trading card arms race. That being said, I like cards, so I picked up a pack. I forgot what was in it (though plasma sword seems familiar for some reason), and I don't care because it was only four bucks. However from a practical standpoint, you will go through numerous mutation fluxes and find tech at a much faster rate than you do items in D&D, so this makes it so, sooo much easier for a DM to juggle. I'd go fucking insane if I had to randomly roll and explain 3-4 magic items after every. Single. Encounter.
Whew. That being said, let's move on.
Cards represent mutations or tech, and are parsed as such into separate decks.
Starting with Alpha Mutations, each player starts out by drawing one and keeps it at the ready (higher level characters ready more mutations). Some mutations grants passive benefits, an encounter power, or both. If it has a power you can attempt to overcharge it by making a d20 roll; a 10 or higher means increased effect, while a 9 or less means it backfires somehow.For example, death reading is a psi mutation that let's you touch a corpse and determine its name, how it died, and something it felt was important. If you overcharge it and succeed, you can animate the corpse to be your personal caddy, but if you fail then you experience the subject's death and are both stunned and rendered prone until you save. Sounds harsh, but you know the risks before you take it, and origins grant you a bonus to different mutation categories so you can try to play it safe(er)...if the cards are right. After each encounter, extended rest, or nat 1 you roll triggers an Alpha flux, which means that you ditch one or all of your cards for new ones.
Omega tech are like treasure drops. In most cases players will be able to loot one after each encounter, represented by drawing from the deck. While Omega Tech can break, players can in some instances salvage it if at a sufficient level. This makes it into a permanent item, allowing you to use it every encounter albeit at reduced power. Unlike Alpha Mutations, there's no limit to the amount of tech you can pack within reason. The only time you ditch tech is if you don't want it, barter it/give it away, or it breaks and cannot be salvaged.
On the topic of tech, most of the gear in Gamma World is handled in a very abstract way. You don't pick from various suits of armor or types of weaponry, instead picking items that fit in a general category. For example, you might use ancient plate armor for heavy armor, or a leather duster as light armor. Your katana might be a light melee weapon, while a chain saw is a heavy melee weapon. There's several examples provided for each type, but ultimately it falls to the group to arrive at a mutual conclusion. Really, the only mechanical choices are to have a hand free but deal less damage (or use a shield), or use both hands to deal the most damage. Simple, but perhaps too simple for my tastes.
The rest of the book is devoted to briefly providing some backstory (almost 2 pages...weak), setting details, sample sites, adventure design, monster tactics, and of course monsters. While some more concrete setting detail might have been nice, I've played and read enough post apocalyptic material to get the gist of whats going on, here. The Fallout series is a good place to start, while Shazbot recommends Borderlands. I dunno, after Rifts I'm kind of glad to have a 99% blank slate to work with. I liked the suggestion to use your local area and fuck it up, and will be doing just that for my first game.
There's 30 pages of monsters, and unfortunately each type only gets a single side of a single page, so there's not a lot of variety despite the 10-level cap. They're all statted using the updated layout from Monster Manaul 3, which means that you could easily get away with throwing D&D monsters into the game with little to no modification necessary; in fact, there's a displacer beast nom-nomming on someone near the start of the book, so maybe this was assumed? I would have liked to have seen more "real world" monsters added to the mix, like in D20 Modern. I think that this game would have been a lot better with a DM book that detailed some sample maps and more information on building up the world, as well as a monster book (or at least monster formula). It's a big box, after all.