>>713870919 (OP)Left is UE5 and right is GoldSrc.
Shadows and light give it out fast. I've played enough HL1 and Sven coop for several years to just know which one is original engine.
UE5 has soft looking shadows with lighting, it looks realistic and pretty smooth, while GoldSrc is primitive and got low shadow resolutions which makes them look sharp and very obviously fabricated, and on top of that, the lights go directly to each direction of lighting the area circularly. Circular lighting in this case is UE gimmick, GoldSrc doesn't do that unless you come up with your own adjustments.