I'm a new Kamen Rider fan who's only in his early 20s, so I only recently watched Black. Most KR fans I talked to said that Black was really good, but also warned me about how dated it was. I'm very glad I chose to watch it anyway!
The plot features Kotaro Minami (Played by Tetsuo Kurata) directly after escaping from Golgom, a cult that kidnapped and experimented on himself and his adoptive brother. The story, when it shows up, is very good and kept me entertained the whole way through. The one downside to the storytelling style is how "Monster of the Week" it feels. Most of the time, this isn't an issue. but keep in mind that some episode's villains are more entertaining than others. The soundtrack is fantastic, and my friends and I got genuinely pumped up when the Henshin or Fight themes came on. The acting is pretty typical for the Showa era Riders, which is to say that while the main character and main villains are fantastic, some of the supporting cast and side characters are...not. I personally find that this adds to the charm of the show. ONE LAST WARNING, if you are prone to seizures/epileptic, TREAD CAREFULLY. This is an old show with old special effects, meaning extremely bright flashing lights and high contrast. Other than that, I hope you enjoy the show nearly as much as I did!