Apart from "good", Harry is hard to categorize. But he is by training and inclination an historian, so many of his works have a historical bent. In fact, recently, he has established himself as the king of the "alternate history" branch of science fiction, with works such as Guns of the South and his epic World War series, which is currently in progress.
By the way, he published a number of stories under a pseudonym, which I don't recall just now. He evidently wasn't sure the public was ready for "Turtledove", which I assume must be his real last name.
I enjoyed Guns of the South a lot. If you like twentieth century history better, try his Worldwar Series which, however, is still in progress. If you are less into history at all, you might try NonInterference, which depicts the consequences of violating the Star Trek Prime Directive in what appears to be a harmless way.