Looking at what Wizards has said so for, here is what we know and can guess about Gamma World.
The boxed set contains a 160 page rule book, two poster sized maps, two sheets of cardbord counters, a deck of mutantion cards, a deck of loot cards and charicter sheets.
Here's what I can guess so far:
If this if 4e setting there is going to be a race, level and likely a class system.
Of the 160 page rule book, 30 pages will be on the combat system.
Since the book is in a boxed set and judging by the size; it will be perfect bound.
Thats all I can guess for now.