I've been playing Sang Froid the whole day and it's been fun the entire time. I love the graphics style and the music. The gameplay is very satisfying, especially when a plan works out the way you wanted it.
I think the difficulty level is exactly right. If you want a good weapon, you will need to safe on traps which in turn makes the game harder. So the difficulty level is kind of dynamic.
The game runs very stable for an indie release, I had only one problem so far where the loading screen didn't stop. A minor point that I don't like is the awkward pauses during cutscenes: When two characters are in a heated discussion, there's always a short pause before the next recording starts to play, so it doesn't feel fluid.
I would definitely buy it again.