Jonathan Wolff (UCL) comments in this amusing column from The Guardian; an excerpt:

[G]ood writing captures its reader by means of creating a tension
between the plot and the story. The reader is shown enough of the
narrative sequence to get an impression of what is going on, and to
whet their appetite for more, but much is hidden. Suspense is created,
and the reader is hooked until it is resolved. But before resolution a
skilful writer will have set up another tension to keep the dynamic
moving forward and on we go….

At least in my subject, we teach students to go sub-zero
on the tension scale: to give the game away right from the start. A
detective novel written by a good philosophy student would begin: "In
this novel I shall show that the butler did it." The rest will be just
filling in the details.

Of course, there is also a rather important stylistic element to good writing, and it is striking that many of the most influential philosophers are good–or at least memorable–stylists of one kind or another:  one thinks right away of Quine, Fodor, Nagel, Railton,  among others.  To be sure, there is still lots of badly written but significant philosophy.  And there is even more badly written philosophy that is not significant but has to be read because it is "current."  So it goes in the scholarly life.