Very nice!
Normally these types of puzzle games are too long or get so incredibly difficult that they aren't fun anymore. This avoids both. It's simple, easy to learn, challenging but not too challenging, not too long, and most of all fun! Also, I love how the ending makes you feel like there's more as well as the way that the end was worded had me go back and solve what I needed to. I beat it several times, but I didn't notice any difference after I imput the 3rd code. Overall fantastic job! I'll be on the lookout for more of these.