Well, now, I thought Shad was one of his better stories. I liked the visions of vast eras and infinite time which the story presented, and the anomalies were interesting. It was more readable to me than many a Lovecraft story, too. Wondering more about what your objections to it were.
It's hardly scientific or critically creditable but to be honest I found myself reading sentences over and over trying to figure out what he was saying. I didn't hate it but couldn't wait for it to get over. "Shadow Over Innsmouth" was the complete opposite, a veritable edge-of-the-seater if there ever was one. The best story in his Best Of collection from Ballantine.
Erm, I'd say Lovecraft's worst writing is anything where he's defending the KKK and saying things like this:
"The negro is fundamentally the biological inferior of all White and even Mongolian races, and the Northern people must occasionally be reminded of the danger which they incur in admitting him too freely to the privileges of society and government. …The Birth of a Nation, … is said to furnish a remarkable insight into the methods of the Ku-Klux-Klan, that noble but much maligned band of Southerners who saved half of our country from destruction at the close of the Civil War. The Conservative has not yet witnessed the picture in question, but he has seen both in literary and dramatic form The Clansman, that stirring, though crude and melodramatic story by Rev. Thomas Dixon, Jr., on which The Birth of a Nation is based, and has likewise made a close historical study of the Klu-Klux-Klan, finding as a result of his research nothing but Honour, Chivalry, and Patriotism in the activities of the Invisible Empire. The Klan merely did for the people what the law refused to do, removing the ballot from unfit hands and restoring to the victims of political vindictiveness their natural rights. The alleged lawbreaking of the Klan was committed only by irresponsible miscreants who, after the dissolution of the Order by its Grand Wizard, Gen. Nathan Bedford Forrest, used its weird masks and terrifying costumes to veil their unorganised villainies."