I bought the latest(only so far) DLC. I like it a lot. I got the "User Guide" since the the "Beginner Guide" is apparently just a watered down version of it. $40 is a bit steep, but it has 900 pages with full of instruction, examples, and mini code challenges (Activities) similar to a text book. There are answers for each one at the end of each chapter--which is helpful. As a user I always just poked around with the methods, and never really developed any real grasp of the fundamental capabilities of the engine. Especially as an C++ guy I really wasn't a fan of the procedural nature of BASIC. Now I actually have some respect for it. The lack of documentation on the site is made up for in the "User Guide." I'll write a Steam review when I am done with the book. I honestly couldn't stop reading it and coding the mini activities.
As for the asset packs, those are good too. They come with some basic examples of use cases, and it makes prototyping really fast since I don't need to hunt down sprite sheets or make my own.
Pros: TONS of assets to use. I'm not sure of the liscense, though. Book is great for noobs to coding, and has the potential for reinforcing the fundamentals for a more experienced user.
Cons: Price point is a tad high; I spent ~60 USD with a 25% sale for the User Guide and the two asset packs. Based on reading the table of contents it dosn't look like the book discusses the 3D aspects of the engine--I could be wrong.
TL;DR: User Guide: 8.5/10, for 900 pages of examples and instruction. -1.5 because it doesn't seem to cover 3D.
Asset packs: 8/10, because there is SO MUCH STUFF. -2 points since your stuff will probably look like everyone else's XD, and unclear of liscense.
-mrradd-