Hey thanks for playing! I'm happy to hear you liked the controls, I think I spent half the time of the jam just working on making the "mech-feel" as good as I could. It's cool you clocked the Arma cold war and Cruelty Squad mentions, because two of the biggest inspirations were the wide open tactical shooters like Arma, the old Delta Force games and Terra Nova Strike Force Centauri, and of course Psycho Patrol R, the followup to CS. I was also by the more open Halo CE levels too, especially the original Macworld demo.
The objective was to destroy 3 power cells scattered around the enemy outposts in the valley, and you need to pick up weapons to get more ammo. Did you just not find any of the other weapon pickups or power cells? Maybe it was just explained poorly in-game, but in the itch page description and a voiceover when walking close to the energy barrier it mentions to find the power cells.