DUSK isn't the first indie game to try to be a retro FPS, but it is the first one I'm aware of that actually succeeds. It fits right into the late 90s-early 00s canon in ways that its indie peers like Strafe have only a superficial misunderstanding of and even AAA "throwback" FPSes like Painkiller or Doom 2016 are either unable or unwilling to commit to.
The game's weapons are satisfying to use, effective, and unique enough that they don't feel like also-rans from already existing games. As far as indie FPSes go, "not procedurally generated," would have been good enough for me, but the developer(s) of DUSK put together a pretty decent set of 33 maps. There's a good flow to them without things becoming too linear. Some gimmicks here and there keep things interesting, and a few of them are highly creative and actually impressive to look at in spite of the 1996 aesthetics. The cast of monsters is somewhat mediocre, unfortunately. It just feels like a lot of ideas being thrown at the wall to see what sticks, with monsters failing to coalesce into distinct roles that serve a greater package.
What surprised me the most was how DUSK managed to cultivate its own identity despite being a direct homage to other, more famous games. It certainly owes a lot to the likes of Quake and Blood, but it also seems to pull a significant amount of aesthetic influence from actual horror titles (specifically, Half Life horror mods like Cry of Fear). The way the tone will shift back and forth between iD-style tongue-in-cheek splatter schlock and genuine spookiness leads to an interesting whole.
I really recommend DUSK. It's certainly no Quake or Doom. I mean, what is? But it's definitely as good as, say, Soldier of Fortune.