It's one of the most influential magical girl anime and Tomoko loved it as a child. Watched by me, today... it's fine, but it's clearly a children's show. It's the kind of thing you might put on in the background. Nothing wrong with it and it can be amusing, but it's not really doing anything heavier.
...well, except for the episode when the 12-year-old heroine gets killed by a truck. No, I'm not joking. The sponsor pulled the funding because they hadn't been selling enough spin-off toys, even though the show itself was doing great. This pissed off the production team. They pushed Momo under a truck full of toys, then the show's main writer wrote about all this in detail in OUT Magazine. (This was back in the old days when creators were kept on a less strict leash.)
Bizarrely, the episode that kills Momo then continues with a musical sequence. It's quite fun. But the studio still had more episodes to make, so they brought Momo back with reality warping powers. As you do. (Momo's second incarnation is fully human, whereas previously she'd been only pretending to be her human parents' child. She was really a princess from the magical land of Fenarinarsa, sent to revive mankind's hopes and dreams.)
Anyway, at the time, it was a bit groundbreaking. Toei Animation had competely owned the magical girl genre until Ashi Pro came along with this show and reinvented things. Momo had talking animal friends (being basically a gender-swapped Momotarou), more chances to kick arse and lead action sequences (excluding Cutey Honey from comparison here), lots of transformation sequences and cool stuff (a car that turns into a helicopter, a magical stick, etc.) She also had a pretty hot transformed adult form and the anime attracted a significant adult male fanbase, which was also unprecedented at the time.
This show was Ashi Pro's signature hit. It also did pretty well in Europe, Latin America and Australia, although not the USA. It's also notable for being an early collaboration between director Kunihiko Yuyama and writer Takeshi Shudo, who later created a small thing you might have heard of called Pokemon.
The show reminds me of a more wholesome Cutey Honey, albeit nowhere near as dramatic. Momo's main gimmick is her ability to transform into lots of adult forms, despite being a small child. She can do anything. Cars, helicopters, football, baseball, machine guns, fist fights, you name it. Momo's unbeatable at them all. She also gets crossovers and parodies. Momo's childhood friends include Dracula, Frankenstein's monster and the Mummy. She either meets or transforms into a version of James Bond, Lupin III, Tarzan, Snow White, Bruce Lee, Peter Pan, Santa Claus, Dr Strangelove and more. The show's too light-hearted to be taken very seriously, but you'll have noticed that it's not afraid to go mental. The tone lets them get away with anything. Some bloke in ep.9 turns to drink and gets an alcohol problem. Baddies threaten people with knives. The best (i.e. craziest) episodes made Misaki and Natsuki laugh, e.g. the stray cat army in ep.11 or the Wacky Races in ep.14. Momo's mother steals crashed car parts and builds a super-bike to participate in a race in ep.28 and do a crocodile wall of death.
The show's unpredictable. Magical girl shows tend to follow a template, but a Minky Momo episode won't necessarily have baddies (or a serious plot). Some episodes have fight scenes, but they're not mandatory.
DISTRESSING OBSERVATION: there's said to be a Curse of Minky Momo. After the infamous truck episode aired, there was a seismic earthquake. In 1995, the series was repeated and the truck episode's repeat broadcast coincided with the Great Hanshin Earthquake, in which over 6000 people died. In 2013, a fourteen-year-old livestreamer who used Minky Momo as her profile picture committed suicide during one of her livestreams, in which she used to play the show's theme song on her piano.
If you're an adult, is this show worth hunting down? No. If you're checking out 1960s or 1970s anime (and this is close enough), I'd suggest sticking with Leiji Matsumoto and Go Nagai. The more I see of their contemporaries, the more impressed I am with what those two achieved. This show's appeal for its target audience is easy to see, though. A little girl can do anything because she can transform into any kind of adult she wants! Also, her parents (both human and Fenarinarsan) don't treat her as a china doll, but instead give her freedom and always trust her to do stuff. It's cool and empowering. Sometimes it's funny. Just don't give your full attention to every episode from start to finish, because it's not that kind of show.