Think I have to agree with eishiya, the background looks sort of much more realistic than the foreground, so it looks a bit weird. I think most of the issue there is the very squarish tiles you have going on. Try rounding those corner tiles a bit and such. Make the tiles a bit more organic, using less straight lines etc. Especially in the back tiles. I mean since you dont interact with them and dont need a straight platform on any of them, you can just go wild with it.(Tried to include it a bit in the edit)
Also I think the characters kind of dont fit in with it all too. I think the best way to fix it would be to tweak the tileset a little. Maybe give it a slightly darker outline around it. Basically give the outline to everything that is a main foreground element and is interactable with in any way. And the grassy part of the tileset I feel is too brigh, you could show a little depth by leaving only the very top brighter and making the sides a bit darker sort of like in the quick edit I made here.
Good job overall on it though! I like the monster animation especially!
