In the first one, the goomba is kinda misshapen, and the top of the pipe looks flat, due to the way you shaded it. The bottom half of the pipe looks better.
I don't see much hue shifting in that second one. Also, there seems to be some banding around some things in it.
The third one, the slime thingies also look rough, and the hole in the building, especially the cracks surrounding it, don't look right.
The last one is, I think, the best one here, though it's not very interesting. You might wanna up the contrast on the door a bit.
I hope some of that was useful.
Here's some quick changes I've done. It's late though, so I'm gonna get some sleep. The old ones are on the right.
You convey volume poorly in the first one. It looks like you're shading on a 2D plane, and not in 3D.
The slimes in the iso city aren't in an iso perspective/grid, so they look out of place, and they don't have shadows. Don't try cracks just yet, they are terribly complicated!
The house looks very flat and the shadow makes no sense. The chimney looks out of place.
As for the second piece... you tried hue shifting?
The pipe in the first picture has 2 lightsources, and the bottom half is shaded more in depth than the top. All the white shine isn't needed, and the grass has no depth + an extremely repetitive pattern.
I like your color choice though.
but it looks same with some mistakes but really a nice work!!!
Okay, I've worked on the Goomba a little bit. I still think Chris is right though; it doesn't seem 3D enough. Does anyone have any ideas, suggestions, etc. on how to make it look better?
I suppose I was completely wrong saying hue shifting. I guess it was just a mess around. Also, by what do you mean an isometric grid?
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<--- The palette, if anyone wants it.
goomba shouldn't have that white highlight; basically, only shiny stuff (like glass, metal, smoosh plastic) emits white highlight. I suggest changing it into a light brown, correcly hueshifted, to substitute that.
I'd like to stick to the palette as much as I can. Perhaps if I dither the white?
unless these are right under a strong lightsource wich is clearly not the case, you don't even need that white.
hell, the blocks look even more flat with that highlight you gave them. you know that if you're going to shade them like that, each brick has its own surface isntead of just being a texture painted on a box. wich means every brick on the block will have a highlight and will cast a shade that will subtly fade away as it gets less exposure from the lightsource.
the goomba is an organic being, if we consider it has a "skin", then it can't wear such a noticeable highliht either. at most, it can have a shadow. not to mention, i don't know what particular expresion you were trying to do, but its certainly not working.
as for the pipe, you might need to get a reference as to how such a lightsource may affect a cilinder because right now it doesnt make sense and its not following the rest of the enviroment.
overall, there's a huge clash going on this piece. you're aiming for a more realistic, less cartoonish shading(not implying that hue shifting or cartoon-like shading doesnt follow real lightsource rules), but the desing itself doesn't support it. even if you perfectly shaded everything and gave it a 3D look that would make it a render, the goomba isn't(for example) having any interaction with its enviroment, nor its afected by it. the way he's standing on the pipe sugest he'd be trying to keep his balance to not fall, or at least try to get out of the pipe. those blocks would cast a shadow on the ground, so would the pipe.
i'm going to asume that the canvas's size was set just to avoid working on a more detailed piece(and it would make sense) but right now its just too small, limiting what could be done with this and its also afecting how the object's proportions are displayed, leaving no room for them to have some sort of life instead of just being stickers pasted on a wall.
and please, do not dither. just don't do it.