Some details...
1). All PC's start at 4th level (or at least 4th level equivalents)
2). One character class - the Explorer (d10 Hit Die)
3). 5 Basic Character Types
A). Pure-Strain Human
B). Mutated Human
C). "Clicky" - in essence insectoid based mutants
D). "Hairy" - in essence animal based mutants
E). "Scaly" - in essence lizard based mutants
4). 74? Random Mutations (and their point values) if you are familiar with previous editions of GW you will recognize most of these mutations. I will answer specific queries about them, but will not list them all. Interestingly enough you can use a "Feat" slot to "buff" your mutations.
5). 35? Random Defects (and their point values) again if you are familiar with previous editions of GW you will recognize most if not all of the defects. See above for queries.
6). New Skills - Psychic Attack and Tech (only PSH's can take Tech as a skill)
7). New Feats - not much here...Powered Armor Proficiency, Multishot (General), and Relic Weapon Group Proficiency (General).
8). Omega Weapons - Hybrid (Primitive) Weapon Table (i.e. makeshift weapons - using an steam iron as a weapon)
9). Omega Armor - (Primitive) Armor Table (Cloth, Leather, Half Metal - Studded, Metal - Scale, Small Shield, Large Shield)
10). Reserve Point System - Alternative HP recovery system
11). Psychic Attack, Force Field, Radiation, Poison. and Fre-Form XP rules
12). Relic Status Table (this is pretty cool) determines relic quality
13). Relic Drugs (9 in all) includes Alertness Booster, Anti-Radiation Serum, Anti-Toxin, Haste Inhaler, Immune System Booster, Muscle Booster, Restoration Fluid, Rubber Flesh (healing potion), and Sustenance Pill.
14). Relic Energy Cells - Atomic and Chemical
15). Relic Grenades - Black Blast (a black ray grenade), Blaster, Frag, Stun, Torc, and Wave (EMP-like effect)
16.) Relic Guns - Blaster pistol and rifle, Gunpowder pistol and rifle, Laser pistol and rifle, Flamer, Sonic pistol and rifle, Stun pistol and rifle, Black Ray pistol and rifle, Torc rifle, and Wave pistol and rifle.
17). Relic Melee Weapons - Vibro blade, Energy mace, Stun whip, and Laser sword.
18). Relic Tools - Anti-Grav Sled, Communicators, Goggles, Bio Analyzer, Solar Recharger, Sonic Imager, and Tractor Wand.
19). Campaign-Changing Relics - Armageddon Armor (better than Powered Assault Armor), Bubble Car, Jet-Cycle, Life Ray, Minimissile (and launcher - think GW bazooka), Powered Defender Armor, and Powered Assault Armor.
20). Mutated Critters - rules for giving standard creatures mutations and defects (small section - 2 paragraphs)
21). D&D Monsters - using fantasy creatures in Omega World
22). Omega Monsters
A). Androids - Thinker, Warrior, and Worker
B). Ark
C). Badder
D). Blaash
E). Hisser
F). Hoop
G). Hopper
H). Latterbug
I). Orlen
J). Podog
K). Sep
23). Robots
A). Spider Bot
B). Stalker Bot
C). Deathbot and Deathbot Weapons Systems
24). Cryptic Alliances (same as previous GW editions)
A). Archivists
B). Brotherhood of Thought
C). Created
D). Followers of the Voice
E). Friends of Entropy
F). Healers
G). Iron Society
H). Knights of Genetic Purity
I). Radioactivists
J). Ranks of the Fit
K). Restorationists
L). Seekers
M). Seekers
N). Zoopremacists
25). Savages and NPCs
26). Domes, Widerness. and Special Encounters
27). Campaigns and Campaign Themes