I think the game would benefit from having specific color that went with each number. Sometimes it was hard to tell if I already hit a number or not. As others have mentioned, it is a very challenging game!
I considered adding different colors, but I felt it would take the challenge out of the 212212212 section of the first level.
I agree with your assessment about the level of challenge. I haven't been able to do the 4 key 4 lock part at the end of level 1.
