Koola’s scenes use photo-realistic materials that offer a bit more of a visual variety within the textures themselves , and reflections/specularity/detailed shadows help fill in the visual space as well. Not to mention that each shot is taken with the most flattering composition possible. Also all of his scenes do include secondary visual elements (some props, trees, windows). No, it’s not a lot, but it goes a long way in making it feel more real and alive. Immersion is very important. What are the guards protecting? Why are they down in the sewer? What kind of world is it? What’s the state of the area the player is in? Is it a slum with graffiti and garbage thrown about? Have refugees or homeless taken up residence in the sewer?
The reason people are bringing up the fact that the scene really needs more visual elements to break it up is because even once you have super nice lighting and shadows you’ll still have an empty space with only one tiling texture. Lighting won’t fix that.
As for issues you have with lighting/post. It’s hard to say. What is your lighting setup? The (what I assume are) lights in the ceiling themselves do look a little harsh, but the light they cast otherwise seems fine. You can create more mood (and thus a better looking scene) by maybe toning down the bounces and intensity and adding some more secondary lighting scattered throughout. A post volume is also a quick way to bring the visuals up a notch using an LUT map to help level out brights/darks and balance color; though I don’t have a lot of experience in how that will affect performance.
Don’t forget that how materials interact with, and react to, your lighting is just as important as the lighting itself.