Shoot the Moon (SPOILER ALERT)
Wow, this game goes to some very, very dark places. The only reason I'm not giving it a 10/10 is because the story about the road to suicide is pretty uncomfortable--but to be fair maybe that's the mark of good storytelling. Since nobody's mentioned it yet, here's how you get to the secret level. Do not continue reading if you want to find it yourself. I finished every level with the clock, then finished the last level with the clock as well (not sure if that's important). After you touch the green smoke, if you wait a second it'll say "There's always another way" at the bottom of the screen. Just fall into the dark abyss below, and prepare for a seriously disturbing ending.