Pretty damned impressed too, from an initial glance. Wasn't planning on making the switch from 3.5, but I have to say that I may just have to reconsider that. It looks like converting existing 3.5 material will generally be easy and the changes appear (at a glance!) to be pretty good on the whole.
Need to read it in a lot more detail first, though - but first impressions are very good.
It arrived on the 14th, NEW ZEALAND time, but the actual time was 1pm Pacific so they kept their promise of arrival on the release date (PDF release time here was 0500, I got the book at 0800)