I found this engaging. It needs to have a restart menu selection, so you don't have to keep quitting and manually restarting the game. There should also be a second failsafe, if you accidentally let a vampire in, there should be a chance to irradicate it. Perhaps using items which are earned when you correctly allow in a human, those items can be used to fend off a vampire that was accidentally let in. If you run out or use up failsafe items, then if you allow a vampire in, you die.