(review based on r16 version of the book - AFAIK the first one marked as beta & compliant with AngularJS 2.0 beta)
Proper successor of critically well acclaimed, best book for learning AngularJS 1.x - aka "ng-book".
If you think that it follows mindlessly the idea for prev book, you'll be ... surprised. Disappointed? Maybe. It doesn't, because (in theory) ng2 is far more simplier than ng1 (in terms of abstracts & syntax), BUT (what's far worse) ng2book doesn't dive as deeply into implementation details (that were sometimes crucial for ng1 - for instance: in case of routing or injecting into pipeline) as ng-book did. It may sound ridiculous, but it made the book make an impression of being not comprehensive enough ...
Good parts?
1. Definitely everything related to Rx - feeding on Observables (;>) is the default way to inject data into application in the book & it's very well described.
2. It's not a book about TypeScript - it'd be trivial to expand book by half by introducing TS step by step & ... that's great. If you want to learn TypeScript, get a book about that.
3. Converting Angular 1.x to 2.x - it's not a perfect chapter (lot of boring, baseline code to go through ...), but it's VERY appreciated.
I hope that ng-book2 will still get updated with valuable content (i.e.: testing!), but for now - it's strong 4 stars.