I love this! Always want to play a game about armored trains! This makes me really want to make such a game too! I love the idea, the chaotic gameplay, and that music matches so nicely with the game too! Very well done!
So for a bit of feedback I feels like not being able to rearrange the train, and also that unlimited length was very game breaking. By spamming electric carriage the game will be won very easily. You could do stuff like making train length an upgrade of the locomotive etc, would makes the game a bit more harder and more strategic. Another big issue was the upgrade reordered each time one is bought. Although its a nice feature getting the cheapest on the left it really makes the whole upgrading experience worse in my opinion, and I just brainless press the cheapest upgrade every time halfway through the game. Also and not least, the final boss feels really underwhelming. Probably it's not even moving make it not feel like a final boss at all.
Anyway, love you game! Well done and keep on the good work!