I'm positively thrilled.
My only gripe is that I've got a long slog ahead of me to get to the point where I'm using the camera to its full potential, but part of that is perfectionism on my part (like AF adjustments on all my lenses and calibrating the Sekonic and building color profiles and what-not) and the rest will be fun (like learning how to make the most of the new AF system).
I wouldn't have turned up my nose at a few more megapickles, but I'll take all the non-sensor improvements over a marginal (and, in the real world, negligible) bump in IQ. Besides, anything I'd personally really want those extra megapickles for...I can just as easily do a panorama and blow past the measly 100 megapickle range of top-end medium format. Same thing for the bitched-about "lack" of dynamic range; any situation where the native DR of the 5DIII isn't enough it'll be also be (at least) questionable enough with the D800 that you'll be doing HDR with either camera. And the 5DIII makes RAW capture for HDR trivial and even gives you a not-sucky preview JPEG to boot!