Tear down as much of that crap as you can, or sand it off.

Then put up drywall (finished side out), then repaint it or wallpaper it to your liking. You will have yourself a "brand new" wall so to speak, that looks as though it was just built.

My wife and I are preparing to remodel our new house as well, before we move into it, and this is the procedure we'll be going through soon as well, for pretty much the same reason.