I got all three keys, and then I went back to the village to unlock the door, but only two of the keys went in, and the third disappeared. This caused to game to enter an unbeatable state in which there was 1 lock but 0 keys, so I had to restart and collect them again. I think the key disappearing was caused by me talking to the guy at the south part of the locked door room.
I like the concept. The game encourages you to take the fastest route possible. Defeating enemies isn't simply a matter of defeating them, but more of a matter of... well, time. You have to think about the fastest way to beat enemies rather than the safest.
In a game where health and time and the same thing, why are there timed spike traps? It doesn't make sense to have to wait for things to avoid taking damage, because waiting is damage. Instead of waiting, I just took ran through all the spike traps and lost the 5 seconds. The difference between waiting and taking the damage is probably like 2 seconds, but that's not significant enough to make a lasting difference.
My favorite part was the part at the end, but no spoilers! If you haven't played the game yet, give it a shot!