I certainly like the concept of the game, having a moving base you can adjust the speed of and fight off enemies on the move. It's like a more violent Oregon Trail lol.
Like other commenters I assume the speed adjustment was meant to have more use but you didn't have time to finish it, same with the depots, since I noticed the counter on the end screen but never encountered any depot.
I could see this being expanded out into a more solid game, with upgradeable carts of various types, maybe something comparable to Last Train Home but with top down shooting.
Good work, especially for what looks like your first game!