Haven't gotten that far into reading it (currently on Druids), but so far I dig the book. The Origins section, for being just two pages, will definitely be a real game-changer (and probably will create the most discussion online). I'm guessing origin is going to eventually replace the term race.
The way the origin customization is set out, I dig it. An elf will still feel like an elf, a dwarf a dwarf. If someone wants to swap their elven training with longswords for polearms, that's hardly a stretch for elfdom, and could be a great storytelling opportunity.
I find that some of the new class abilities are contingent on DM approval to be interesting. For most of them, I think I'll be requiring a swap of an existing and commensurate ability seems fair. But I also imagine that some DMs will be fine tossing it all in the mix and others none of it.
Also, I was a little iffy on the alt cover, but in person it looks gorgeous. The shimmer gives it a lovely ethereal look.