So I finished it out of sheer obstinance, but I want to say this to all game developers.
If very precise timing is important to your game concept, DON'T USE FLASH!
Flash is a great platform for quick games, but it has drawbacks. Namely, it has a highly unpredictable event model, and it can't guarantee realtime results. That means I'm going to get to the last section of your game where I just got past three monsters and a pit in a row, and suddenly I run into a wall for no other reason than, say, my Flash player decided to run the garbage collector at that moment, or something on my OS decided to page out to disk. So, the whole game, a jerky blur already, jerks again, and there's no possible way other than luck to time the keystroke correctly.
Great game until the last section. But a game that's difficult because of the platform doesn't make your game laudably challenging or hard. It means you made a dumb design decision.