Mission Control has no spaces, background image doesn't change and Launchpad background is dark
Seems like I'm not the first one to hit into this issue, and it is related to Dock process working incorrectly. The easiest way to fix this is to type 

killall Dock


into the Terminal, which will effectively relaunch Dock process (and hopefully fix the problem).

If this doesn't work, reportedly trashing Dock preferences and attempting several restarts may help.