I wouldn't call it completely different, nor 'unsable'. It's a little different, and people don't like change.

They removed "Most Recent". That's the only thing that I use, and most people use on facebook.

I don't like the change, but if they are competing with google by making drastic changes to their interface, then they have a problem.

That's exactly what people said about the news feed, and more recently the chat sidebar (when your browser window is wide enough). I found the chat sidebar annoying too, but after a few days it wasn't jarring at all.

People just use Facebook so much that even small changes trigger massive waves of "OH GOD THIS IS COMPLETELY UNUSABLE" hysteria.