The goal is “fairly hard scifi”. So you get hacking rules (which scifi games seem to be require to have by law, nowadays), game play is focused around fire fights and suppression and the tech is generally on the believable side.
We did aim for more of a “Vietnam in Space” feel, so if you like the feel of something like Stargrunt, you should feel pretty well at home.
The “Alien Battlefields” section does cover hostile atmospheres (increased stress and vulnerability) and unusual gravity but not in exhaustive detail. Just a few flavor rules to make things feel more interesting.
For a full on “moon scape” battle, you’d probably want to elaborate a little bit more, but it’ll serve as a starting point.
I agree with the point about them being a place to start. If you’re the type who ends up house-ruling your games anyway (like many of us) then NSIS is hard not to recommend if you’re looking for a sci fi game with a more “realistic” (whatever that means) feel. At $9.99 I’d say go add it to your digital collection asap.