Hmm....

Cool!

Here are some things that I find important:

- A strong atmosphere and creative/interactive leveldesign with puzzles, I find it no shame if the game has backtracking through levels, it's always fun to revisit and enjoy the mayhem you've caused. Less linear corridors is better and maybe alternative paths or shortcuts and of course secret places and traps.

- Intimidating enemies which are somewhat intelligent and fun to fight (please no aimbot enemies) and have different deathanimations depending on the weapon used against them.

- A lot of weapons (10 or so) which can all be carried at once but are destinctive enough but fun to use and also feel/sound powerful or weak depending on the weapon. Maybe a melee weapon and handgrenades.

The thing that Half-life started was a level design more based on "reality" and thus some bland logic in the sequences of rooms, objects placements and such, it introduced "expectedness" in the genre.

Back in the days, there were a lot of Doom maps shared on magazines cd-roms and such and it was always interesting to test all of them as "amateurs" would rather experiment and put their visions forward (ranging from maps based on the nazi cross to peace&love sign, etc...) rather than caring modern gameplay things like covers and such.....

Of course, with a modern audience, "expect the unexpected" is maybe not the way to go commercially. I would recommend that you do some demo (1-3 levels maximum) to get feedback from random "customers" (post it on gamejolt and itch.io) and in consequence, evaluate the commercial potential (at worse if it doesn't make it, you will at least get some new audience/following)

Just a suggestion, you might want to explain your limits, especially if you're working on this alone. A lot of these guys sound like they're suggesting fairly complicated stuff that you'd only be able to do with:
A. An insane amount of effort
B. A team
C. A good amount of money to buy the software/team necessary
Mind you, I don't know exactly what's involved, but be careful not to sacrifice time or game length too much unless you plan on releasing the thing for free (I don't care if it's an amazing game with HD graphics and the best fight system ever, if it's too short and you charge cash for it, people will complain. A lot.).

Yep, Level Design is what separates older and "modern" FPSs.

Yeah, I'm probably going to go with something more abstract, akin to Doom levels. Give them the IMPRESSION of being a real place, but not get too wrapped up in actually making them look completely real. Kinda like the city levels in Doom 2. You get a rouch idea of what they're supposed to be, but their design is still abstract and interesting. Maybe a little more realistic than that, but that same idea. An interesting layout and look to everything will trup realism.

I'm not THAT concerned about commercial viability, since as I state elsewhere this is really more of a passion project than anything else. My primary goal is to make the kind of game I've wanted to make since I was a teenager. Secondary is to provide a true oldschool FPS experience where it counts, since there are like 2 of those on the market. Basically just Wrack and the RoTT remake.

And hey, it turns out there's an audience for my horror games, so I suspect there's an audience out there for pretty much anything :P

The environment color palette reminds me a lot of MDK. A MDK FPS would be sweet, come to think of it.

Seems quite interesting. The weapons do look pretty good.

I would recommend using much more simplified and stylized textures for the environments, though.

Also: "there is actually a bit of autoaim". Awesome! Would a keyboard-only mode be feasible?

Well, everyone is just giving their ideal view of what a good FPS throwback would be like. I know that some things aren't viable for me as a solo developer. For instance, there's no way you'll be getting HD spritework. I'm not an artist, at best I can fake my way through modeling and texturing. I certainly can't create good sprites. CERTAINLY not good HD sprites. But hey, I agree that would be really cool to see a modern FPS like that, so it's something I might keep in mind for a future project that I might want to actually collab with others on.

That said, if everyone balks at the idea of a game with oldschool 3d visuals, maybe the project should just be a hobby rather than my next planned release.
Hmm... not sure. I mean, technically speaking it is (I think. I'd have to go over the input handling again to make sure), but I'm designing the game around the speed of a mouse, so I don't know if it will actually end up being something that's playable with just a keyboard. I'll keep it in mind, though. If it's easy to implement there's not really any reason not to have it as an option, even if it isn't the "right" way to play.
Regarding textures... is it the overall confusion of the pixels in, for instance, the wood texture that doesn't read well? Just in terms of workflow I want to be able to utilize stock textures without too much per-pixel hand editing for as much as possible, but I might be able to improve things just with some contrast/color changes. And it's not that I'm adverse to hand editing or hand drawing, it's just very time-intensive for me and about half the time the results aren't very good.

I watched the video and I love the sliding move but the textures would need some bit of work because they're too "muddy" and thus they're a bit confusing to what they "represent". Good news is that it wouldn't require a lot of work for you to do this: the trick is to have quickly identifiable patterns which create contrast and would be more appealing. Take a look at how walls and floors were represented back then (of course sometimes it's also muddy in some levels):
http://www.gog.com/game/doom_ii_final_doom
http://www.gog.com/game/rise_of_the_triad__dark_war
http://www.gog.com/game/outlaws_a_handful_of_missions
http://www.gog.com/game/blake_stone_aliens_of_gold

For example, try doing some diamond pattern on a 256x256 canvas then apply a pixelate/mosaic filter (in gimp & co) then downscale to 64x64 for the final texture.

Hmm, so what you're saying is that I actually WANT to have textures that noticibly "tile" at mid-long ranges? Kind of the opposite of what I've tried to do before now, but you might be right. When you say "contrast" I assume that means contrast with other textures around it, right?

EDIT: actually, wait... I think I see what you mean. I went through the textures I've implemented, and the ones that look the best have something in them that is easy to understand (like a brick etc) that can logically repeat over a large area. The wood texture (which I have covering the entire level in that video) doesn't have anything like that.

So carving recognizable "boards" into it would probably solve most of the problem, you think?

I'm slowly getting the feeling that asking the community of what type of game they want is like asking Homer to design a car .
My two cents: do your thing. Some will like it, some will hate it. Adjust to convince the moderates. Success. That's how i did it with Birth of the Empires.

Well sure, I'm not going to be designing based primarily on community feedback, but it's still good to know what other people would be looking for anyway. Like, if the majority of people want something that's the opposite of what I'm planning, maybe it's worth reconsidering.

In-depth story line.
Tons of bosses fight.
Tons of weapon/ weapon customization
A little bit less pixellated graphic.
Variety of dungeon (the jungle, inside a spaceship, the city, subway.. etcetc.)
Better audio sampling.

and boobs.

Then show off a small prototype. At least that way people can give some real feedback without wanting you to create QDukeoom.