Nice use of theme :)
Just a few things to mention:
- The mini-map was way too helpful. It showed what the player could already see and more
- Maybe don't show the laser on the mini-map
- Retrying levels increases the number of Keys Left (by about 8 keys). Even going from Hard to Easy, the number increases
- It's possible to collect a key more than once
- You can only exit if you have exactly 0 keys left - no more, no less