One of the pioneers of the super robot genre, the Getter Robo saga, which started in 1974, still remains one of the pillars of its genre and a major inspiration for many authors.
The story of Getter Robo is fairly simple: a group of 3 teens are summoned to pilot the Getter Robo, a machine that is capable of defeating the monsters that threaten the human race. Each entry in the saga usually has a different main trio, a different Getter, as well as different enemies, but they all have a similar premise and execution. Despite the simplicity, the plot explores several themes and has
dark undertones, which make it interesting. Unfortunately, due to author Ken Ishikawa's death, the story remained unfinished.
Initially, the series was drawn by Go Nagai, while latter installments were drawn by Ken Ishikawa. Both art styles are very similar similar, so the transition feels natural. Also, overall, I'd say the art of this series is pretty good.
The protagonists of Getter Robo are quite interesting, as they are not your usual do-gooders. They each have their individual traits and quirks, which get developed as the story goes on. My favorite from the bunch is Hayato Jin, who is introduced as the intelligent psychopath leader of a group of teenage revolutionaries. Just from this description, you can guess that the protagonists are all far from the usual.
Overall, the series is very enjoyable. I love the GAR and testosterone-fueled battles and I believe the series is worth reading.