I never thought That Old Black Magic was terrible. I mean, it wasn't great, for sure. There are far far worse episodes of the show, though. It's really only our second look or so at Crais, so it has that going for it. His appearances seemed rather rare in the first season for him being the main antagonist.
No, the insight into Crais' character is rather interesting, especially as it's really one of the first indications that you see of the Sebacean race being distinct from the Peacekeeper organization and that the people are not exactly supportive of said organization.... a theme that occurs a few times over the course of the series.
My main problem with the episode is Maldis himself. I feel like he just doesn't work for this kind of series. It was an attempt to try and give Zhaan a more personal villain, but one that I don't think really ended up working out in the end, especially when 'Rhapsody in Blue' does a much better job of giving Zhaan a personal enmity...