Just finished watching the two part "Blood and Fire." It quite closely follows the original novel. There are some changes, of course, by needing to fit within the Star Trek
It's a good story, but there's no way it could have been told in the '60s, at least not with the open depiction of gay characters. But I don't know if that's really relevant to the overall story. It could have been told on TNG, but of course they chose not to do that.