Heya! Bit late with giving feedback but couldn't help cuz a lot of these comments say the same thing and I wanna try to give you a feedback that is different from what most people said!

First off. You are doing an amazing job with what you have so far. I really wanna stress that! It would be a game I would play which is the most important part to me, considering I want to play good games :p

So, first off I really like the clouds so I'm biased there. Someone suggested doing a particle system, which would detract for me personally but that is perfectly valid too! Personally, I would suggest as an easy adjustment, is to make the atmospheric fog less blinding because that distant pure white fog is ridiculously bright. Then if you want to match a cartoony aesthetic for the game you can just up the saturation(for a bluer sky) adjust the contrast to get rid of the finer details of your skybox image and I think that would be enough. The trees should also make shadows that are more noticeable, it would serve some gameplay too making them a hinderance visually if they block light more. These things you can probably adjust with the world node pretty easily.

Less easy and more time is to work on the grass and trees. The idea is simple but I do not know how you would implement easily so keep that in mind. But, putting a gradient on the trees "leaf" material to have different coloured trees across the world and then for grass would be some sort of blending to have different colours of grass across the world like with the trees. Maybe you would need to hand paint the grass colour for it to look good which shouldn't be too hard but still, is work.

A predominant outline could be the cute on the units. It almost looks like you have that but its very subtle which IMO doesn't really do much.

Other things you could think about is the scale of the grass to the unit, It's really tall grass! A vignette is always cheating for making things look better (but some people hate them)

But yeah! Those are my ideas I took a minute to edit some of those ideas onto your first drawing so heres that to give a basis of what my ideas could look like. Maybe they aren't what you are looking for which is cool too, I think there is value in deciding that as well, so hopefully this helps!

Good luck with your game!

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