I was pleasantly surprised at this La Petite Mort entry. It's dark enough to be a great EctoComp entry, but the violence and theme isn't gratuitous.
It is short, and the transitions between different planes of existence were executed quite seamlessly. It doesn't have much in the way of puzzles and is linear and straightforward, but does give the reader a modicum of control as to how they would want the ending to play out.
I must admit that I tried to do things way darker than the storyline intended :). The game didn't respond to these, but it was fun exploring them!