Minami Kotaro and Nobuhiko Akizuki grew up together, as close as brothers, having been born at the exact same time and their fathers having been best friends. Together with their sisters Katsumi and Kyoko they experienced an idyllic youth and wanted for nothing. All that changed though on their 19th birthday, wherein they discovered their fathers were members of the sinister Golgom cult and that their births took place at just the right moment during a solar eclipse to mark them as Century Kings, candidates to become the new Creation King for Golgom and conquer the world. Minami Kotaro manages to escape before he can be brainwashed and thus is able to use the powers forced upon him as Black Sun to fight as Kamen Rider Black! But can he rescue Nobuhiko before he is transformed mind, body, and soul into Shadow Moon?
Kamen Rider Black occupies an interesting position in the Kamen Rider Franchise; it aired from 1987 to 1988, 3 years after the Kamen Rider ZX TV-special and 7 years after the Kamen Rider Super-1 TV-series, and was conceived as a stand-alone series that would not require any knowledge of any previous entry in the Kamen Rider franchise. Because of this, it makes for a good entry point into the older Kamen Rider shows that aired before the 2000 revival series Kamen Rider Kuuga.
Visually, the show is very very good; the Kamen Rider Black suit is really well put together, featuring areas of organic tissue at the joints that really sells the idea that Minami Kotaro is physically transforming and not just putting on a suit. The monster suits are also really, really good with with a lot of well thought out detail and use of materials that makes them look really organic and natural. The Golgom lair and the high priests also have a really good aesthetic, sinister and ominous. The fight scenes are also really well done with good camera angles and choreography. The only exception is the opening and ending credits, which are the most tepidly dull things I have ever seen; seriously, the opening credits is Kamen Rider Black getting on his motorcycle and riding it and the ending credits is him getting off his motorcycle and walking towards the camera. That's it. Also, I would be remiss if I did not mention that the show really likes to make use of strobe-light effects in its stock footage, so if that would be a problem for you please keep it in mind.
Musically, the show is a bit more mixed; all the tracks and songs are really well done, but the direction and timing of the songs, particularly in fight scenes, can be pretty off; sometimes they change songs six times in a single fight or otherwise they play the energetic heroic music when Black is getting his ass kicked.
Minami Kotaro is a very good lead, almost entirely by virtue by how enthusiastic his actor is and how much effort he puts into the role. Kyoko and Katsumi unfortunately don't really get much to do until the final third of the show, but when the show does make use of them its generally good. The Golgom High Priests Daraom, Baraom, and Bishium are pretty much interchangeable but they are a good villain group. The Sword Saint Birugenia, despite obviously being a spur-of-the-moment addition to the show, is a very fun and active villain with a good sense of panache. Shadow Moon is great, there is a very good reason why this guy is regarded as one of the most memorable Kamen Rider villains in the franchise's history.
Story wise however, is where the show really lets itself down. From what I understand, the guy who was supposed to be the head-writer left the show after episode 12 and there were in the end about ten different writers for all the various episodes, so there's a reason why the show meanders so much and has no clear idea of what it wants to be. This problem is mostly resolved in the final third of the show, but that's still a lot tedious and poorly paced plots to have to get through before the show can truly begin. Plus, the ending is good in some regards, but in others is so ridiculously cliche that those elements have been parodied perfectly since then, so hmm.
Basically, Kamen Rider Black is a good show, but it is not a great one.