try adding 3 wheels or four to the vehicle to aid stability and aim for power over speed, and lower the centre of gravity slightly but still have a bit of room for the hills so you dont get grounded :D
needs a reset button to return vehicle back to original and maybe a few buttons that allow you to switch between layers, gets a bit tricky to try and click the item you want but 4/5 for effort and 4/5 for orginality
cant believe the inventory price is so high, having to constantly leave items because cant pick them up.... maybe have a teleport system where you can port out to the town and sell items then port back in to where you left?
the time between units is far too long hence the 2 stars, maybe reduce the time it takes because the ai seem to be able to produce faster on single barracks/archery buildings :(