First things first, the aesthetic is on point! Second, my GTX-670 is running at 25-30 FPS steady in bigger areas like the sewers or forest. 60FPS when at home base.
Oh, and the way health works confused me, as when I saw the HP, I expected it to dwindle instead of acting like a Paper Mario style health point.
Sewers: The sewers are a pretty good introduction to how exploration is rewarded. The environment interaction is also pretty fun.
Forest: Hoo boy. That tank in the beginning of the map? if it finds you (and it probably will), it'll lob grenade rounds your way until you get past the jumping puzzle, which is pretty interesting in execution minus getting hit with a series of lucky shots.
Then comes the blind forest part. Radar comes in clutch, but if you didn't know there would be enemies, prepare to fend them off if not beat them with the shotty because the rifle does jack to them besides stun.
Suggestions:
1. Limit the angle that the tank can shoot at so that you're safe when you're at the treetops.
2. I concur with Retsa that the ranged enemies don't really look for you, but I have been spotted once or twice in the sewers.
3. Have the shotgun use a more traditional walljump type detection for the secondary fire so you don't feel like you're trying to use a finnicky rocket jump.