Well, that isn't the only thing. I guess what others might complain about is the lack of composition, structured use of color, etc.

As much as paintings look similar, generated ones do not have a proper structure, the applied colors do not match the original intent and are often misplaced.

One of the obvious flaws is the reflection of the houses in the water, the painting isn't structured and the system isn't capable of discovering that kind of structure.

Paper on the other hand shows a very nice method of finding unique filters from given examples, and the results are amazing.

There's a lot of knowledge required to make a good painting besides just knowledge of other good paintings. I think it would take a long time and a huge neural net to encode those principals without human level intelligence.