What an addictive little game. The difficulty curve makes the game feel manageable, and could maybe even be a little faster. It feels incredibly slow to have to start over once you've got a decent number of upgrades. Visually, the aesthetics feel like they're from 3-4 different games: It's a cute little choo choo roaming around a Zelda II overworld shooting guns at chibi demon puffballs lol. That said, I'm sure you intended on adding more weapon types to justify buying wagons and turrets separately, and the gameplay itself is a lot of fun!