It was running on a pretty old engine. It was based on the Quake 1 engine, but some features of the Quake 2 engine got tacked on along the way. There was some more eye candy added as well, but something with that basis isn’t going to be as power hungry as Unreal.
Really does run on everything (lemmy.world) angielski
Half-Life 25th Anniversary Update (half-life.com) angielski