I'm assuming you did the work for everything on this city. There are a lot of shortcuts with your pixel work, and it's showing. The grass doesn't look like grass. There are no blades, and the highlights are random blobs. It might work as a dirt or rock tile if it was cleaned up a little. Far too many things on this have noise or dithering when it doesn't need it. The cars expecially. I like the line work on the van, but the dither kills it for me. It's supposed to be metal, go ahead and give it a shine.
It's very obvious what brush you used to make the pine trees. I'd suggest looking at real pictures of trees and then looking at how other pixel artist you admire do it. The other trees have a better shape, but since they use the same colors as the grass (or close too it) it blends in. I didn't even see them at first.
The cement ramp looks pretty good. It looks like it's made of cement, which I don't think I could pull off. The inside needs more dithering to make it a smooth curve. Right now it has a very obvious line. With the other ramps you should try dithering it yourself instead of putting a gradient in, reducing and letting your program put the dither in for you. Right now if it weren't for the black outlines they'd look like they were all made from sand. Though the middle ramp isn't so bad.
The black outlines are random and a bit jarring. You should pick one or the other. Though it does look like they're only there for the WIP parts, which is good.
Those are the things that stood out. A little work will go a long way with this one. Keep at it!
