The episode is an 8/10 without the ending, but the ending loses a point. Grampa makes a speech about needing to be cranky. Suddenly, the dose somehow makes no effect. It also takes 17 minutes to show us those eyes. Sure, they're disturbing, but that's no excuse to finally set up the plot when there are only 5 minutes left.
Otherwise a great episode but that ending...7/10.
Otherwise a great episode but that ending...7/10.