Suggestions pasted from conversation over Steam as per Draco Nihil's request.
Overall I have very positive feelings about this but I'd see more horror feel rather than some terrorist assholes having to attack the player.
1. The tiling of the texture on the ground is off. I'd stretch it a bit, maybe. Or make a texture 2x the size or choose one that tiles more seamlessly. Looks like a series of bright spots. The texture has a visible bright circle in it - darken it and it'll look better already.
2. Also, I believe Proph's suggestion is grand: make more stuff destroyable. Walls, windows... give the monsters option to try breaking into the house, to make the feel complete.
3. I think that for SP version you could use friendly marines from RySpak (I think they're from there at least) - it'd be fun to have marines as bot pals, dunno why I feel this way (just fan of the UMS overall I think). You mentioned an smarine playerpawn of yours - the player could use it for the full feel. Player marine, supporters also marines. Grand.
4. Also. the landscape feels empty - maybe a dried dead tree here and there? I remember seeing the meshes somewhere.
5. Realistic weapons are a good idea but I think there should be a chainsaw too. Maybe the one from UT (UTWeapons boasts all guns from UT, including the chainsaw). IDK, always when people are trapped in desolate houses, if the screenplay guys mean business, they add a chainsaw.
6. I am planning to have my modelling teammate make a skeleton nali enemy, based on the RTNP decoration. You could add these for example if you wish to wait for them. Like the Book with no Name or many a zombie horror.
7. Also, may I recommend adding an option of a finite amount of rounds for people who want to win no matter what. The last round would be so-called breakout round. An evac vehicle would arrive by air or by river if you add one and you'd have to break through to it. This final wave would've been endless as in: no pauses but more and more enemies coming and you MUST escape because you can't hold on any longer.
8. Also, crappy Skybox actually isn't crappy. If you can, make the cloud movement speed up a bit with each wave so that the last wave is really frantic, like in these horror movies when an old deity is about to show up.
I'm wondering if I should have a distant ruined city visible in the skybox.
No, that clouded dark sky is perfecly enough - a ruin, even in the distance, would ruin (sic!) the feel of "middle of nowhere"; i1f you have distinct landmarks even in distance, it ain't the middle of nowhere anymore.
The sky is going to be yellowish, something to look like being in a polluted wasteland.
What makes you think polluted wasteland has yellowish sky? Sky of a polluted wasteland would be exactly that - dark. Why? Because most forms of pollution shit stuff into the atmosphere making light less easy to come by and thus everything darker.