I really enjoyed this as a prototype --- there's a wonderful kernel of risk/reward of picking up more parts and cars and balancing speed with defensive capability.
Most of what I read in the feedback I'd echo, with one exception: I actually liked that the it was difficult to pick up cars when you're moving too fast, because that means that even speed has negative tradeoff to consider. I wasn't expecting that from the outset and was pleasantly surprised by it. (The placement issues on the other hand were definitely genuine).
It could be the RNG that I got, but not many offensive turrets dropped for me. I would have loved if the demo had really gone a little overboard by the end (even at the expense of balance) to highlight a train decked out with turrets and a screen full of projectiles ---- Or, sell it in presentation with particle effects, screen shakes and other "juice" to make the scene of a 'chaos train' truly feel like power to be reckoned with.
Thanks for sharing and good luck in the jam!