Volume
So I'm bored out of my mind waiting for Red Dead 2 so I decided to go through my library again but with the sound turned up as high as possible without my eardrums exploding and fuck me does it make games a lot more exciting and fun. Anything with guns or explosions actually feels like it has impact now, they're fucking loud and startling and it makes it feel a whole lot more real.
Even for more easygoing, downbeat games it adds a lot. Try it out and post results.