I can’t tell if these were intentional or if they’re bugs. If the former, I wouldn’t say they’re improvements. 
- When you climb up the elevator shaft to find the guard asking what the zombies are, his animation is way too static. In the mod, he moves his head up when he says “Gordon!”, and leans forward a bit moving his arms when he says “What the hell are these things, man?” Basically he has natural movements as he first speaks to you. In the Steam version he doesn’t move his body at all. He’s like a statue.
- In the mod, the ghostly sound that plays during the title screen begins as the title appears, sort of fading in with it. When I played the Steam version, there was a fairly large delay between the title appearing, and the sound playing. Can’t tell if it was lag or something.