I'm now playing level 17 to test for difficulty
Here's some updates I made to the weapons that I'm hoping will improve gameplay. These updates should not affect how easy or how hard the first 5 levels are:
* Bullets now do 4 damage
* The chaingun will waste 2 bullets (The first 2 bullets do no damage), and then until the trigger is released bullets will do full damage.
* If you hold the 2nd button for the handgun, bullets will continue firing. The handgun is about half the speed of the chaingun (even if you fire bullets by pressing 2nd repeatedly), but of course you don't waste any bullets.
* The rocket launcher requires more safety distance, but will do less damage if you're too close to an object.
At this point, I would say that the handgun is better for enemies with a health bar initally halfway full, and the chaingun is better for the rest. At least, that's my goal.