The rule book is actually quite extensive - it's 103 pages divided into eight main sections. Off the bat it's actually really great to see the amount of fluff in this rule book. In recent times GW have been moving away from fluff in rule books, but this book has a solid 30 pages or so of dedicated fluff and that doesn't include the gang backgrounds. You could see it as a much expanded version of the White Dwarf article from last month - we're taken through the Houses, the history of different Hives on Necromunda, the Spires, teased with some cool background on political machinations, get a tantalising glimpse of the Imperial Fists garrison on Necromunda, have Eldar, Squats and Beastmen all mentioned plus the gangs from the old game fleshed out in quite good detail. Overall this is a great part of the book and gives lots of ideas, pointing to possible Genestealer Cults, mutants and mentions Psykers quite a lot.
Speaking of gang backgrounds it does need to be said that there are only rules in the boxed set for making either Escher or Goliath gangs. if you're doing something fun like Dark Eldar slavers or even any of the legacy gangs, this rule book will not give you the answers you're after - there are clues though.
Basically you have 1500 points to form your gang. The gang members vary in price depending on the gang and their role (Leader/ Champion or Ganger) then you add the price of the weapons they carry. The more weapons or exotic load outs, the less gang members you can have. You are restricted to between 0-2 Champions and of course only one Leader, but the rest can be fleshed out as Gangers. In the old days people would have two tiers of Gangers, the well armed ones, and then Juves who would be less well armed but fill out the lower points you needed to have to get to 1500.
As well as basic rules there is also an Underhive Armoury secton on the weapons of the Underhive (mainly for Escher and Goliaths) and then some missions, which are set out in a very similar style to the old Space Hulk missions.
As far as GW rule books go, this is a good one but it's areal shame that they didn't include a generic Gang Bulider system so all those people whop are busily hobbying in preparation, and I have to say that the majority of people we've talked to ARE making their own gangs, can't use them straight out of this box.
Now that being said, this morning there has been a PDF released for the Legacy Gangs of Necromunda - from House Orlock to Cawdor - which will give all of us a basis to make our gangs using the weapon profiles and points costs. This is a great service ot the Community and good to see that GW have seen the buzz and paid attention to it so the hobby element of this game isn't lost! (File attached below)