Actually Coop on Portal 2 have great replay value.
Get a friend who havent completed Coop maps yet, load it up and let him solve it for you. Refuse to do anything until he tells you to do something. On some levels it get REALLY hilarious.
Here I was browsing available games on steam when I come over this:
The year is 1942. Adolf Hitler has succeeded in resurrecting dinosaurs. The reptilian horde has trampled Europe and the Mediterranean. Can nothing stop the Nazi?s dinosaur army?
If that isnt the most wicked...