The top row that used to have thumbnails of individual desktops, now just has text.
Mission Control Is Terrible, Exposé + Spaces Had It Right
Andrew Hainen

I totally feel your pain. I miss Exposé & Spaces. A quick work-around to restore the OSX Lion Mission Control (with Thumbnails) is Hot Corners. I set the Top Left Hot Corner to activate Mission Control and Boom! Thumbnails are shown instead of text. Hope this helps.