not bad
Well first I should state that the eye candy is very nice, and the controls work well, but the only problems I found were relatively minor ones.
If you were to make a sequel, I would suggest the following upgrades:
-the gas depletion is the biggest problem that I noticed while playing. After the dwarves start comign constantly, you simply don't have enough time to refuel. Cut down on the gas depletion rate, or put gaps in the enemy waves.
-add a level system, with different maps. The hardest oens shoudl have dwarves comign from both sides. Include tunnels (where you can't attack them) and maybe a bit more weapon variation. It would be nice if our machine gun thing fired a little in front of the helicopter instead of straight down.
-label what the numbers at the top represent. I figured it out eventually, but you didn't explain it anywhere.
-add a minimap so you can see where all dwarves and flags are.
-also add some more powerful opponents that take a few hits to bring down.
Overall good job though. Good potenial if you feel like making another.