Red One! Green Two! Blue Three! Yellow Four! Pink Five! Coudenshi! Bioman!
Five hundred years ago the Bio Robo arrived on Earth and showered five young people with Bio Particles, that they might one day save the Earth from the fate which had befallen the Bio Star. Now, the year is 1984 and the evil Dr. Man, ruler of the Neo Empire Gear, has begun his campaign of conquest. In response, the Bio Robo and its caretaker Peebo awaken and gather the five descendents of those who'd originally received the Bio Particles and charge them with becoming Biomen to save the Earth!
Note that the version I watched was the English dub that was broadcast in the Philippines, which in addition to changing many of the names was also hilariously awkward for the first several episodes. However it is not a deal-breaker and certainly could have been far worse.
Choudenshi Bioman was in many ways an experimental Super Sentai series; for one thing, Bioman was the first sentai to feature two women on the team, and what badass ladies these women were! In fact, Mika/Yellow Four was the first member of the team to receive an individual character focus episode, and ended up being the first to get a truly badass moment of awesome out of the whole cast. However, after episode 9 her actress seemingly disappeared off the face of the Earth; there were lots of rumors about what had happened to her, but what we do know is that the writers had to act very quickly; Mika was killed off in a heroic and was swiftly replaced by the second Yellow Four, Jun...who proved to be an even greater badass than her predecessor and was quite possibly the most badass sentai warrior for a long time. While Hikaru/Pink Five was not on the same tier as Jun, she was nevertheless quite capable and they got multiple episodes together and apart to showcase that they were the true breakout stars of the series.
Another innovative factor to Bioman was how the Monster of the Week worked; rather then having a new monster that grew to giant size at the end of the episode, there were instead five recurring regular monsters, the Beastnoids, with each episode having a new giant robot called Mecha-Gigans. There were many occasions where the Mecha-Gigan was integral to Dr. Man's schemes and the plot of the episode, but there were a few times when the Robot was just tossed in at the end so that the Bio-Robo would have something to fight. Also, halfway through the series Dr. Man upgrades his arsenal all-around, upgrading each of his minions while sending out Neo-Mecha-Gigans, which unlike their predecessors would be piloted by one of the Big Three, his lieutenants.
Plus, unlike most sentais both the Bioman team and the Bio Robo possess multiple finishing moves, which is very nice. However, at the halfway mark, just as Dr. Man is stepping up his game, the Bioman team increases its power, resulting in one finishing move repeated for the rest of the series. At least they're nice and impressive looking.
Finally, the ultimate victory over Dr. Man is not achieved through superior firepower, but through appealing to the tiny vestiges of humanity remaining within him. Not an ending you hardly ever see in a program like this.
The tone of the series is on the whole quite light; occasions like the death of the first Yellow Four are the exception to the rule. Even the arrival of the sinister Bio Hunter Silver, destroyer of the Bio Star, doesn't really do much to change this, even if he was a good addition to the show's dynamic.
Bioman is not as impressive as it could have been though; character development on the whole is very light, with Shingo/Green Two and Ryuta/Blue Three often blurring together, and despite recurring throughout the series, neither the five Beastnoids nor the Big Three get any appreciable development. There's also a lot of episodic filler with preachy lessons of the day for the younger viewers. Furthermore, a one-shot character named Shota Yamamori is teased as a possible sixth member late in the series, but ultimately is denied which was a real shame considering not only that he had a ton of personality but was also teased as a possible love interest for Jun. Finally, there comes a point where mention is made of Dr. Man's former wife, and while their son ultimately plays a significant role in the end, she does not. That was the only real disappointment I had with the endgame.
On the whole, Bioman is quite good and definitely worth watching.