A few words about style and inspiration
TL;DR: We like comic books!
One thing we've heard a lot about GrimKeep is "That reminds me of [most commonly Darkest Dungeon]". If you're working in any visual arts field, you're probably used to this. Brains are pattern matching machines, and when presented with stimuli, it will spit out the closest or sometimes most recent match it has. Sometimes to hilariously off-the-mark comparisons!
So, what was the inspiration for the art style in GrimKeep?
The truth is that the end result is an amalgamation of many things. Let's break it down:
Most obvious - the drawing style
Once we had settled that it needed to be a 2.5D game, we intended to explore various styles, but one of the first tests was based on older fantasy comics like "Savage Sword of Conan" and others from that era. The brightest shining artist from that group, is John Buscema, although many greats have illustrated comics in that era and style.
Immediately after doing the first test drawings inspired by this style, we felt that it was 100% right for us, so we just stuck with it. Quick not about inspiration; we're not putting a lot of energy into copying exactly how these comic book greats drew. We know we're not the crème de la crème of that style. It's a starting point, and we're using some of their techniques, but we're our own artists, and we're using different tools and have different constraints. So apologies to Mr Buscema and his colleagues for the blasphemies we commit! :)
The colors and values
Something that took a bit longer to settle on was which colors and values (how light or dark it is). In the beginning there were a lot of reds in the drawings and the UI. But as we were fleshing out what kind of world the game takes place in, it wasn't quite right. We eventually settled on unhealthy greens, greys, and browns. The greens represent the eldritch, the lovecraft-esque monstrosities. The greys and browns represent the dystopian reality of a world without hope. Also, grey is a backdrop color, something that lets other more saturated colors draw the attention of the viewer. Browns are low saturation orange and red, which is complementary to green. You could almost say that it's basically a green game, and the rest is just supporting those greens.
We do allow ourselves to use any color we want for highlights, accents and color pops, but the general impression should be towards greens. Art direction is to a large degree self-imposed restrictions, and so far, we're pretty pleased with the ones we've picked.
There's also values. I guess it's pretty clear that GrimKeep is a dark game. Not just in setting and theme, but also in value. It's probably no surprise that we'd avoid brightness and strong colors in a dystopic setting like ours. But finding the right balance have taken some doing. It also forced David to implement Gamma settings very early in the project. We have had a few awkward presentations where a screenshot that looks great on a high quality screen in a shaded room, apparently becomes just a dark grey square on a projector in a lit room!
Finally, all these 2D assets are all put together in a 3D scene in Unity. Here we have some tools at our disposal that the comic book artists of the 70s and 80s didn't have. We (mostly Samuel to be fair) add lights, effects, and some post processing. These are very nice things to have, that adds life to what is essentially still images.
User Interface
The UI has its own style, separate from the art. It took many iterations to settle on it. We tried to make it in the same drawn style. We tried several versions of highly rendered material-based elements. Nothing really clicked until in a fit of inspired frustration, Henrik did a quick test with very flat UI elements, focusing on the color, values, silhouette and dropshadows.
Most of the effort goes into tweaking and testing the values of the individual elements, to make sure it is in its right place in the "attention hierarchy". UI needs to be clear, readable, and obvious most of the time, but aesthetically it should not overpower the art, the environments, the characters.
Every screen is a delicate balance act of what draws the attention of the viewer, and in what order.
Item icons
Another major part of GrimKeep is the "items" that you equip on your journey.
These are drawn similarly to how we draw the characters, but with a bigger focus on readability and them fitting neatly into the item slots. They could represent any object, which can present a challenge. In particular long and thin items like a sword or spear, would be at very small scale if you're trying to fit them into a small square. With these we take some liberties, and show the most significant part only. 
See this in action
If you're curious, on our various socials we regularly post timelapses of the artists drawing.
Check them out on Youtube, Tiktok, Instagram or Bluesky.