I really liked the idea of a train that drops you off into a combat zone and provides support.
My only issue with the game was the difficulty. It was way too easy which actually confused me a bit since it made me question the point of any of the pickups. When I saw more mechs coming out of the train I thought it was a glitch until I realized what was happening. Same with energy, I just never seemed to run out and was kinda confused as to the purpose of the batteries.
Seeing other comments mention that the game was difficult makes me think I exploited it a bit. I think the map is just big enough to easily run circles around the enemies and avoid bullets. It might be better if the map had obstacles, like instead of an empty field it could be some military base or village overrun by insect monsters.
Being able to control the little dude that drives the mech is a nice touch, but I think it would be cool to have the player start as just the human and force them to collect parts to create the mech. Obviously this would require a lot of balancing and testing to work right which is difficult to do during a jam.
I also found a glitch on my 2nd playthrough where after getting into the mech, the little zoom in animation played but the mech sprite just stayed in front of the train. I could walk around and shoot but I was invisible.
Overall great entry. It was fun, polished, and had great art and music!