You know, it's one of the first games i've been reviewing that i genuinely liked. The only thing that i didn't really like though was that it would crash sometimes for no apparent reason, but that's not actually reviewing the game, so let's move on.
Basically, i was attracted by the fact it has some resource managing going on, like a manual tower defense game, that feels more satisfying to play because you're the one shooting the enemies. Not sure if you had this on mind or it's already implemented in the game, but i think the game would be better if you got bullets faster if you don't shoot for a while. If you did implement it you should add a value that displays how quickly you're recharging 'darkness'. Pickups would also be a plus!.
Also, not really something negative but i played the game for a while and i think there was some point that enemies came so often you had to let in at least one enemy -happened to me at least 2 times-. I kinda felt really sad that there was no score because i'd be playing this to get the top score on my devteam lol. Good job, mate!