Yeah actually, good idea with the kill counter / score! (I mean, in its current state there's a set amount of enemies each time so you'd always end up with the same score, unless each attack gave different score or something...)
By the way, I really didn't make it clear as I kind of just rushed it in in the last half an hour, but you end the game by attacking the "corruption source" (big blobby thing) on the right that becomes accessible after killing all enemies. Thanks!