It’s a long time ago now so my recollection is likely very flawed, but with HL I didn’t like the feeling of a created path that must be followed, irrespective how of the interleaving of different aspects. There are lots of modern games like this too - which on the face of it are relatively open-world, but underneath the apparent freedom there’s a strict path to find and follow for success. (I’d definitely include one of the modern Doom games —I forget which it was I tried— in this category, - it was so linear that it felt but one step removed from the old-fashioned shooters where you’re literally on a conveyor belt and shoot whatever appears.)

In the original Doom, in contrast, the only requirement was to make it to the end of the level, figuring out the map and puzzles along the way. Anything else (did you chase 100% kill and 100% secrets?) was optional. I guess it just felt more… honest?