I'm about 40 pages in. So SPOILERS are included in what I've read so far...
I'm liking it so far. I love how the book is filling in the cracks, like the Tessio execuition and the tid-bits about roughing up the kids who raped Bonasara's daughter from the beginning of Part I.
I don't know how I feel about Michael flying a plane and Fredo being gay though. We'll see.