This is a very worthwhile book on MTB technique/skills. I would say it is quite biased towards the downhill/jumping/slalom side of things, which isn't surprising considering Brian Lopes' background.
So you get lots of good information on cornering fast, jumping, drop-offs and general stuff involving unweighting the front wheel (wheelies, bunnyhops and other BMXy stuff). What you don't get is info on riding mud, roots, tricky uphill singletrack with mixed obstacles etc, or long distance trail riding, or fitness training.
The info you get is very good IMO. I certainly started to understand how the writers integrate dynamic loading and unloading with almost all their techniques to jump, corner harder, gain speed, increase traction and more. I'd not thought of it like this before and it's spot on.
The language is a bit "gnarly dude" hip but even an old codger like me understands what they are getting at.