I think the surround sound mixes are really good. They don't seem to suffer from the overused compression that the stereo mixes received.
Sadly, I really don't have the opportunity to listen to the 5.1 mixes nearly as much as I do stereo versions, so my go-tos are a variety of versions.
The new mixes of the live albums are a significant improvement over the originals and the 1994 remasters.
The green box albums are generally a marked improvement over previous versions too, though the odd mistake here and there are distracting.
The red box albums are better than the originals, (especially Invisible Touch and Genesis) though once again the slight changes are distracting.
Of the blue box albums the only one I prefer over the 1994 remasters is And Then There Were Three. Abacab seems to sound like Abacab no matter which version I hear but the 1994 remasters of Trick, Wind, and Duke are by far my favorite versions of those albums.
I know a lot of folks were disappointed in the 2007 remixes, but I appreciate what they accomplished even though they aren't perfect. As far as I'm concerned it's nice to be able to choose from several different mixes and masterings in order to put together my own personal "definitive" series of Genesis albums.