I have made the plants taller and the fields shape a square; EDIT: I have also made straight up:
And the reason why the existing graphics look "bad" is the fact that they don't have any shading whatsoever, are pixelated because they were upscaled at some point and generaly don't fit the style which was introduced with the building and worker graphics. So even if graphics aren't bad by themselves, the can look bad in the overall composition because they pop out or the visuals are a "mess" as whole.
The worst offender I could find via a quick search is this one:
While (some) graphics look fine for themselves, the way they are thrown together make them look bad.
On the other hand this games has probably the simplest possible graphics but they look "nice" because the fit together.