Awesome game, I loved this. The music was great, as was the gameplay. A few things that I noticed that could be improved:
The menu at the beginning took too long to load (pointed out before, I know).
The game tended to start lagging badly for me after level 20, and reducing the quality and turning off the effects did nothing to improve it. Closing the window and loading my save reduced the lag to zero, though, even though I had all the quality settings back on.
When I reopened the game on lvl 37, I found that it hadn't saved my auto-repairs ( I had bought up to level 4). This was very expensive and I barely survived the level so that I could buy new ones.
At one point, I somehow managed to buy all the machine gun upgrades, including the one that wasn't available to me at that time, for nothing. I don't know how it happened, but after one of the levels I looked at the list and the machine gun was fully upgraded.