Just wanted to say that Penumbra: Requiem is released (a while ago actually!). It is an expansion to Penumbra: Black Plague and focuses more on puzzlse. We have also tried to make the most of the physics and make fun puzzles using it.
Here is a trailer:
http://www.gametrailers.com/player/40366.html
The game uses Newton 1.53 since it uses an older version of our engine. The new engine have Newton 2.0 implemented (as seen in a character demo I uploaded a while ago).