one thing that sticks out is an inconsistency in styles. for example, the wood stuff has less colors and more contrast than the bricks and the grass, which makes it stand out a lot. likewise, the dirt looks strange next to the soft grass. that kind of thing.
I like the texture on the bricks a lot. imo though for the angled walls you could do something like this to better show the depth:
(obv i did it sloppy and just changed the brightness really quick but i think it shows the idea)
you said "no shadows in this mockup" but idk if this is what you mean or you meant something else. if you have other plans for that kind of thing then all good.
also this:
yours | mine
again super sloppy, but the way that you did the tilted brick looks awkward and unnatural. something like this would angle it in a more realistic way.
I notice the tiling in the grass texture; there's a repeating dark horizontal line. It's suble and something maybe only a perfectionist would pick up, but maybe worth mentioning.