I finally got a copy, and there isn't all that much background information in it. Given the number of typos, errors, and inconsistencies, I'm not sure I'd consider all of it to be canon. They wanted the book to be available when the game came out, so it went to press before everything was finished.
There are a number of differences between the book and the game; some are improvements, others are interesting ideas that got left out. The karma ranks (every 250 points) were going to have a more significant effect: positive karma would give a bonus to AC and damage, while negative karma gives a bonus to HP and damage.
The art for many of the new weapons was very 'flat', seen from the side rather than in an angled perspective. The needler pistol and gauss rifle look completely different. Most of the small guns use short 3-round bursts, so the P90c and FN FAL don't empty the magazine in just two attacks. The P90c also uses 9mm ammo as the name implies, and regular shotguns have a double-barrel firing mode. The G11E is considered a big gun and has a bipod attached. The gauss rifle is an assault rifle, doing less damage but has a burst attack. Same for the pulse rifle - less damage, 3-round burst. The knife, combat knife, and sledgehammer have distinct swing and thrust attacks: knives can be swung faster, but thrusts are significantly more damaging; the reverse is true for sledgehammers.
In Broken Hills, anti-mutant conspirators are supposed to be using the underground tunnels, so they're filled with minor traps, not giant ants, and the large chamber in the southeast is used as a storeroom. In New Reno, Richard Wright is a well-known drug user, which makes the jet overdose and finding a canister in his room much more plausible.
In the SAD, there are six or so Mr. Handys in the robot repair bay. Whenever you leave a level, they take the side elevator there and fix any damaged robots. It's not clear if that means just healing injured ones or completely repairing destroyed bots. The laser tripwire is supposed to do nothing at all - that's not a bug or unimplemented feature.
At the Wanamingo mine in Redding, the elevator goes down only one level, not all the way to the queen 'mingo, and you have to fix the generator to get it working first. Also, you have to clear out all the vermin above ground (rats, then Morton's gang) before you can sell the deed back to the mayor. When the Mole Rat Mambo runs out of rats to fight, it gets changed into something more exciting - Deathclaw Deathmatch.
There are some other differences, but they're not as significant.