Well, there are three versions. The original is about a team of bird themed costume superheroes who use ninja skills and high tech gadgets to stop a terrorist organization called Galactor who wants to rule/destroy the world.
It is loosely inspired by American superheroes (most notably the costumes which have a Neal Adams Batman feel. Even Tatsuo Yoshida admitted he was given a comic by a US GI in Okinawa and took it home with him, he was fascinated by it and decided to do his creation in that style)
It is also the first to feature original elements that would coincidentally transfer over to the Super Sentai series 4 years later in 1975. (wrist morphers, team of five, finisher to destroy the monster, personlized individual weapons and a team attack) The series has two spin offs, an OVA, a flash animation comedy show, a live action movie (which isn't very good) and a slew of merchandise. The first series is available for free on Hulu if you are curious. The others are sadly only available on less legit measures due to licensing issues caused by the next one.
The second is the various dubs/adaptations: Battle of the Planets, G-Force etc. They are part of the reason the west even knows what anime is, as many older generations watched those on TV as kids and that paved the way for more anime to come over. Most play fast and loose with the content to appeal to an American audience and are commercially available in some cases.
The third is Gatchaman Crowds, a re-imagining of the franchise for the digital age with social commentary on how we use the Internet and Social Media. It may irritate purists as the bird motif is replaced by shiny neon Tony Stark armors, but it is an interesting take on how our digital world can affect us as humans and analyzes how superheroes would work in the age of Facebook and Twitter. You can view Crowds on Crunchyroll.