Good idea - but could be better
This game is really a godd idea. Big plus for that. The gameplay, however, is terrible. Not terrible, but terrible compared to the potential. Add more vehicles, and fix some bugs, and you're on the way. Also, remove the homer - it obstructs more than helping - it blows you away when you try to hit things. Due to this, I usually don't upgrade it at all.
Also another thing that annoys me is the fuel limit. Because of that, I can't do combos bigger than a certain amount, and it also pisses me off when I lose the game because I can't land due to a large amount of homers and miners shooting me up into the air. Add a buffer to that, so that duel doesn't run out while in the air - or that all it does is kill your engine, so you can't move - you'll just fall down tot he ground (and of course continue to gather points if you hit anything before you get down).