RBDOOM-3-BFG VS dxx-rebirth

RBDoom3bfg, same thing, but for the BFG edition.

On the other hand BFG edition supports 120Hz rendering and has some great gamepad support. However the "shoulder lamp" and some tweaked brighter lighting destroys the game's atmosphere IMO while some textures and lights appear worse. I'd still recommend it if you liked the original game, but perhaps also play it with RBDoomBFG and its GI datapak - it introduced PBR shaders and changes the lighting considerably, but the game wasn't designed for that so i'd recommend it only for a second playthrough (you can disable most of the effects but even then it still looks off). The official BFG edition is closer to the original Doom 3 but still has its own issues so unless you want 120Hz rendering and/or gamepad support, i'd still recommend the original (with Dhewm3). Also note that the original BFG edition doesn't allow you to skip cutscenes which is annoying for a second playthrough.

BFG has better out of the box support, but both versions are open source and as such the community has made source ports for both of them to the point they are essentially equivalent and you only pick the one with the features you want the most, last time I played was using BFG because RBDOOM3 added support for PBR so the game isn't so absurdly dark but your mileage may vary and may prefer dhewm3's more faithful experience using the original release

And that's the first level of Descent. :) I literally just started a brand-new game yesterday of Descent. DX-Rebirth.

Find a remake of the game ported to a modern engine. https://www.dxx-rebirth.com/ appears to be a port of Descent 1 and 2 to the Source engine. It won't help with you running the 3DFX version, of course, but this might actually be better?

I loved this game. You can still play it with DXX Rebirth

I would look at DXX rebirth, https://www.dxx-rebirth.com even if you just want to add the expansions to your steam version, you should be able to use its instructions to add the levels to your version.

Descent 2 - so long since I last played any Descent game I forgot how the experience was, but hey there's a source port!

Or if you still want to play the originals, the DXX Rebirth mods also make it easy to play on modern computers!