The art doesn't even need more detail or realism, it just needs consistent detail.
Even just a simple palettization/pixelation preprocessing for every sprite could be enough - https://i.imgur.com/oPH7paD.jpg
And making sure light is consistent. In the first picture some objects like banners, notice board, bathtub shaped thing have clear shadow below them, others like fence, green plant, mushroom don't. Buckets have light coming from left side hay stack from right, other from top. I wonder if it would look better if some objects were flipped horizontally.
That's at least 50% of it, if he had given his artists any direction it should be this: Light coming from top left, soft shadows. Give the artists a palette and let them create. When you don't have any limits, your creativity is unbounded, and that can be bad for delivering something on a time budget.
That is a surprisingly good result. It literally changed my perception of those screenshots from "that is some gross and sloppy artwork, I'm keeping my money" to "hey not bad, I might buy that"
