This is a pretty good read.
Greene does digress into silly analogies and painfully remedial mathematical lessons from time to time.
Nevertheless, the many flavors of conceivable "multiverses" are an interesting and quite modern topic.
Greene acts like a used car salesman at times, using syrupy language to give speculation more than it's due.

Worst of all is his "giving equal time" to the anthropic principle!
Anthropic arguments are nothing more than an "I give up" approach to explaining the yet-to-be-explained.
ANY FREE PARAMETER can be pointed at with an up-turned nose, and labeled a "problem with the theory".
The free parameter can then easily, and without fail, be "explained" using an anthropic argument.
Why does [insert any free parameter of any theory here] have the value that it does? Maybe we're just lucky!
You've solved nothing. No possible unique prediction can be made by anthropic reasoning alone.
Any unique prediction can be made WITHOUT anthropic reasoning. It's useless. Worse than useless. It's wrong!

The description of the measurement problem was good.
The description of the holographic principle was good.

I was really surprised by one assertion: Copenhagen and Many Worlds have different predictions. Greene argues that in Many Worlds, the wave-function have multiple spikes, corresponding to different possible outcomes. He reasons that these "spiked waves" might interfere, causing an observable interference pattern, which would disagree with Copenhagen wave function collapse. He admits that decoherence makes this "an extraordinarily formidable task", but I'm not sure what he means by this! Is it formidable to do the calculations, or formidable to measure them? He states his clear belief that Copenhagen and Many Worlds are, in fact, distinct theories, but doesn't at ALL explain how he reached this conclusion. Every source I've ever read treats them as interpretations which make the SAME predictions. In this case, I certainly do NOT take his word for it, and neither should you, fellow reader...

The end of the book devolves quickly into child-like nonsense philosophy like the "ultimate multiverse" where "math is reality" and every possible equation gets it's own universe... Honestly, I don't know why the publisher let Greene put this frivolity in an otherwise serious book.