I managed to get the game stuck by collecting the exit too soon after beating the boss. I think probably the "Foe Obliterated" text interacted badly with the end screen, so that's something to keep in mind for the future.
Based on your description on this page, something changes when you do multiple runs? If so, then I think you should explain that in the game.
In general I think you should go bigger with effects since I didn't really notice them. If you haven't watched, in Mark Brown's Day 2 stream he talks about this (at 27 minutes playing Drivey Trucks)