Also, I remember that quote (from Gabe himself, I think): "We may have polished graphics further, but that game won't be Half Life anymore.", a direct stab taken at linearity of Doom of that time.
Of course, 'theoretical' hardware limitations aren't hard limits -- they're soft[ware] ones. However, if you find yourself battling concrete hardware limitations, what you need is to put your back into it and a little know-how.
Valve said "Ha, let's see!" and implemented great HDR visuals with integers only. So it's not just let's hack together and see how it goes. IIRC, it took three re-implementations to get it right and performant.
Similarly, I'm not a stranger when it comes to hardware and its limits, but what deemed impossible by many, even knowledgeable people, doesn't mean it's a hard, cold truth (e.g. demoscene and PoC||GTFO).
I think mine came with Vietcong, which was... underwhelming.
I still listen to it on occasion. Don’t even remember how I found that song because I’ve never played that game, I don’t think.
And now two short decades later we're paying 10x the amount for top-tier cards, and HL3 still isn't out.