I got my new forest green K-S2 yesterday, so I haven't had time to take images in the field with it yet but here are my first impressions:
It replaces my K10D and K-x, being more compact than the K10D but thicker and beefier than the K-x and with an excellent handgrip. It's very nice with big and chunky lenses, like the DA 17-70 f/4 AL SDM that was unpleasant and front heavy on my tiny K-x but now is a very comfortable and lovely combination with the K-S2, this is my preferred standard zoom.
Build quality is excellent, the swingable back screen is really useful and viewfinder is smashing. Tons of settings to make and it's easy adjustable to one's own preferences. It really gives me K10D features in a smaller and more compact package, without being too small. It lacks the AA-filter too, like the K-3, and it has the same adjustable AA-filter simulation. Sure some options are in the menu instead of on separate buttons and controls, the K10D (and K-3) has more external controls, but thank's to user modes and programmable buttons one can make settings that gives easy access to DOF-preview etc.
All in all I'm very happy so far, and see no real point (for me) to go for a K-3.
Only thing I don't like is the black plastic shutter button, it was shiny chrome metal on my K10D...