The fact that you are making something original, and that each image has a purpose makes it more interesting than a mash of 3D renders. I know for myself I like more stylized 2D characters, and I find that I really like it when I can see the line art of the art. So I would definitely look into a game when it uses custom art like what you are making.
I see you are putting in some extra detail by adding in shading with contour hatching. One thing I've struggled with is coloring, not just color theory, but I find coloring a image even if its just flat tones ends up distracting away from good line art, which contradicts with how good art can be when colored or even shaded. I know for myself I've debated how much time and effort to put into coloring art just because while I do like nice line art, sometimes color is important to describe a character's personality or mood. IE what color is the bedroom, their hair, their eyes? But then spending time on this requires more effort for every art piece and trying to figure out energy and time priorities. one thing I wanted to do when I get back into more art focused work is to be very light with my color, treat it like a water painting... but I need more tests before I figure if it will work with my interests or if its too much effort.
An example of very basic shading that I might suggest is with the first image, looking up at Helen. I like exaggerated art, being good at exaggerating art means being good at controlling the players attention and focus, very hard to do when using a 3D model as a base because the 3D can be very stiff. But what can be done is to make the legs and but lighter, and dim the upper body so that the attention is on the 'closer' object. Which I guess this brings up another issue with line art in general, while line art can show of one's skill and design, unless you like to play with line weights, its hard to know what to focus on in an art piece. I like your example with her on a bed, because even though you aren't doing too much with the line weight, it is somewhat noticeable, but more importantly, the fact that only she is shaded helps draw attention to her and pull out of the background noise.
Wow, these are exactly my thoughts mostly! The second paragraph was my thinking process when coming up with this art style. Initially I wanted the colored art with smooth shading, but when I tried coloring it, I noticed that the character of the line faded so very much that I just decided to not color anything. Plus it takes time, to make it worse, basically (in my case). Then I tried something like a drop of a color here and there, for the imagination to fill the rest, because yeah, the color tells a story big time, but I liked it more the way the images look now. If I were a more experienced artist, I may have succeeded in coming up with a good subtle coloring, but my art skills are very poor.
I don't actually draw these, I make lines above the reference pictures I made with 3d models in VAM game. I could have just used the base screenshots, but there are problems with collisions, etc., and I liked it very much how the line art accentuates what I want to accentuate. And I can modify things if needed.
It was actually a big doubt for me if I should use such pictures, because technically they are not "art", just lines over screenshots.
Hence the bad shading. I don't understand the anatomy and volumes great to make it good. But I think it looks good enough to be playable, and I'm interested more in making a game than becoming a good artist after a couple more years during which I actually wanted to make games.
You noticed correctly about the line weight. I simply use a bigger brush size for things that are closer and a lower brush size as they move away from the player. Or less important, like the environment. And yeah, I shaded only the character, because I wanted to accentuate the attention, and basically who would be interested in the room? I assume that the only thing the room is there for is to mark it's existence. Nobody is gonna examine it. They will probably just note the surroundings by swift glancing over them, and then examine the character.
And for the shading, basically the same. A make more shading where I want more attention. And a make it blackier for the points where the attention should go. By the way I noticed it improves the art like 10 times. Just adding the black points where the cavities are.