Very polished experience overall! Love the look and feel of it all. I really wish that you could have taken advantage to let you be able to play this with the 10 key numpad on the keyboard! I understand that would have been a decent amount more work though.
The UI in particular is very good and the puzzles are good also, if not fairly repetitive. This is definitely a game I will play a few levels at a time and come back later.
Thank you for giving a Music off setting too because the lone track gets very repetitive very quickly!
Overall a very nice experience, great job with the theme also!