The use of a passive voice bogs down the flow, making for a dry and remote presentation. Also over use of references and notes. Too superficial, personal, or glib. The subject matter is often lightweight, or is buried in material that isn't relevant to the thesis or story. Examples and analogies are not compelling or relevant.
Author tries too hard to entertain the reader.
Author often uses too many personal references and sounds amateurish. Too technical or instructional. Your colleagues may understand what you are saying, and you may think it shouldn't take an Einstein to understand you, but the average reader needs your lexicon of terms translated into simple English. The text often remote and ignores the fact that there is a reader. It also lacks clear examples.