There is another thing that hasn't been discussed yet. This is a major thing for me, as I'm italian, so English is not my mother tongue.
Sometimes it happens that an author becomes so caught up with the plot, that he changes his style, his way of writing.
Readability is very important for me, as I have to put up a double effort to read a story: following the plot, and mentally translating it while I'm reading, because I'm still not so versed in English to be able to think directly in English words, I still have to translate each and every sentence to be able to mentally picture every character and situation.
Sometimes it happens. You start to read a story that flows through your brain effortlessly, you fall in love with the characters, and then it happens. Reading becomes a real challenge. It gives you a headache. For two totally different reasons.
One. The style becomes too much simple. I'm speaking here from an italian point of view: italian language has something like about half a million of different words. We're used to name each thing with its name. If the author's style becomes something like "That dude did that thing with the other thing", I have some problem to figure out what exactly the author is meaning, as English language is known to have completely different meanings associated with the same word, and only the context of the sentence is the key to pinpoint the exact meaning of the word. With the italian language, we're not used to this. Almost everything has it's own different name. So, too few words is bad.
Two. Italian language has something like about half a million of different words, but we don't use all of them. So, if the author becames too self-aware of his deftness with lexis and the development of the plot becomes more a stylistic performance than anything else, with a new and different word for every line of text, the result is that I have to spend more time on the dictionary than on the story, and that's another headache. So, too many words is bad.
Also, if the sequence of tenses is wrong, or if there are too many grammatical mistakes, that also doesn't help the mental translation, and the flowing of the reading.
And that's it. This is my bit. For me it's disturbing the kind of change of the writing style, that slows down the reading too much.
Maybe that's not so relevant for and English-language born reader, but if you have to translate each and every sentence while you're reading... you come to like authors that have the right ideas, and they express them in the right way, with a writing that's easy to read: accurate, not too poor and not to sophisticated.
And that's another form of balance.