This is genuinely excellent, I really enjoyed reading it.
You managed to fit a ton in without any of the pages feeling crowded. The tight NPC descriptions are especially well-done.
Only suggestions:
- Differentiate the guns more and open them up beyond fighter/rogue. In a setting that's basically guns-only, locking half the classes from using guns hurts the feel. I think you could get far by adding more guns and splitting them differently. Obviously you were space-limited here, but if you go back I'd expand that. Something like:
- Fighter: Carbine, rifle, revolver, derringer
- Priest: Rifle, derringer
- Rogue: Revolver, derringer
- Wizard: Derringer
- The functionality of gunner badges feels weird. They represent your skill, but you just buy them? And as only fighters/rogues can use them, this puts fighters/rogues at +6 AC compared to priests/wizards for most combats here. Not sure what, but I think some refinement is needed there.
- I found the force-field functionality a bit unclear, especially on the aliens stat-block. Not so unclear I'd have trouble running it, but I think I'd actually be just making up half the rules.
Anyways, that's my effort at constructive criticism. Excellent adventure.