I wish you could control the speed of the minecart with A and D the same way you can in the level select. This also would have been a good way to make the difficulty adjustable (slower for more time, faster for more challenge).
I'm pretty bad at this game (couldn't beat level 6), so even when I was able to hit all the boulders, I would still die because they were close enough to the track to hit me. I probably tried that level about 20 times before I gave up.
Still fun while it lasted nonetheless.