This release really has had a focus on stability and bugfixing. I've been running the betas and rcs, and unlike previous pre-releases, I didn't notice any regressions at all this time. There wasn't a whole lot of new features leaping out either, but the emphasis on bug-fixing was evident, with some bugs going back to the kde 3.5 era (!!) finally being fixed! =:^)
In particular, I've appreciated the fixes in kwin and konsole. The biggest single bugfix for me was in konsole, which added support for two wide-terminal mouse protocol extensions, finally "unbreaking" mc when used at the far right of wide-screen konsole sessions. When I saw that bug-fix/wishlist-item going into then 4.9-targeted "trunk" shortly before the pre-beta1 freeze, I knew for sure I was going to be running the betas this round! But like I said, even beta1 went surprisingly smoothly.
Now, being a gentooer, I better go, as I have some building to do! =:^)
(FWIW, one of the things a good gentooer appreciates is the ability to do things like entirely opt-out of semantic-desktop at build-time. It's precisely that kind of control that makes the hassle of scripted build-from-source worth it. =:^)