Half Life 2 was released over 20 years ago. It was meant to run on what is now regarded as ancient hardware.
When Half Life 2 released there was actually a whole lot of grumbling from gamers as the system requirements were very high. It ran like shit or didn’t ran at all unless you had very recent and high end hardware.
I remember buying a new gpu back then specifically because of HL2. I didn’t have a lot of money, so I bought an Asus 6800 card, which wasn’t powerful enough to run HL2. However with a bit of luck those could be modded and overclocked into an 6800 Ultra which was powerful enough. However it was a lottery whether this was possible and ran without issues. The first card I bought couldn’t do it, so I went to the shop and returned it. Went to another shop and bought one there, which also didn’t work. Then I went over to another town and bought one there which finally worked out. Even though it was a mid-tier card, gpus were expensive back then so it cost me all of the money I’d saved up for a couple of years before.
HL2 has gotten a lot of optimizations as the years went on, but when it first released it was an example of an unoptimized game when released. And just like these days people were bitching about it.
Absolutely, they pushed the limits on what was possible and used everything they had to make something really unique. They also wrote the book on level design with the Half Life series. If people haven’t seen it already I would recommend this YouTube docu about Black Mesa which goes into detail about the level design aspect: https://youtu.be/G_TcAxAKCAI
One of the things Valve also did really well was to have a quick and easy update system. This allowed them to push updates out to users quickly and fix a lot of bugs and optimise the game. This is taken for granted these days and even hated as devs push out unfinished unoptimised games with the promise to fix it. But back then this was a new thing and a lot of people were very happy about it.