Good writing has a specific audience in mind and tries to relate to that audience.
Good writing is interesting and engaging. When I read good writing, I come away feeling like I learned something new or read something beautiful. It's fun to read (I think it's possible to make even boring scientific papers at least a little fun to read.)
Good writing provides details, enough to be interesting and instructive, but not details that are irrelevant or inappropriate for the audience. You don't want to overwhelm the reader.
Good writing has a logical flow and a structure that makes it easy for the reader to follow.
Good writing is concise and precise (not the same thing). You want to use just enough words to convey your meaning. You want to be clear in conveying your thoughts (especially important in scientific writing). If you are having trouble writing a sentence and have the choice between being more concise or being more precise, I would always choose precision, because the content of your writing is more important than the style.
Good writing has music and personality in it. Maybe there are a few exceptions, like writing an instruction manual, but I think it's possible to incorporate "music" and "personality" into research papers. It's very hard to be interested in writing that is dry and abstract. I'm no expert on this, but there are ways to make your writing more dynamic. You can vary the lengths of your sentences and the constructions of your sentences. In classical music, you notice that the tempo of the music changes, or the key switches from major to minor. You can do similar things in writing.