I like the idea, the look, the logic and the gameplay... in fact, I like the game... Good work!
P.S.: about the speed (I noticed you complained about it in the description), there is few tricks to make it noticeably faster. [To optimize speed on any ZX81 Sinclair Basic program is probably the thing I like the most... it might be the reason I like this machine so much.] If you want, we can exchange on the topic... after the contest I guess. ^^