Regarding the Enter not working, it could be. The Enter key management wasn't perfect, so the correct popup button could lose focus, and then the Enter key does nothing.
There are 10 levels. Description updated. After you do some tries, it feels easier. My best strategy is, don't rush on the first levels, as there's plenty of time. On level 7 you have to start rushing a bit and use the Enter key to close popups. It needs some tries, like most difficult games. (Added the "difficult" and "permadeath" tags too :P). Thanks for your feedback!
After seeing your other comment, I updated the description with the number of levels to beat the game. You were right, it's easy to give up when there's such permadeath and you don't know when the reward to win the game will be.
