Love Live! School Idol Project (2014-15) ran for two unexpectedly successful seasons and a movie, before ending in a Definitely No Sequel fashion. This is that sequel. It achieves this by having an all-new cast in an all-new school, doing mostly the same things we saw in the first series. They're fans of "mu"s, the original show's heroines, and they're trying to follow in their foosteps.
(You don't have to have watched the parent series, by the way. It stands alone just fine.)
It's a cut-and-paste, to be honest. It's nearly the same show again. However I don't mind that at all, because I enjoyed both shows and this one might be better-written. It has more character development. I'm not in a hurry to watch idol shows in general, but every so often they're capable of being fantastic (e.g. THE iDOLM@STER) and this one has the added bonus of not really being a proper idol show. They're schoolgirls in an after-school club. They're doing it for fun and/or to drum up publicity to save their schools, not as a (vapid, unhealthy) career.
The main difference is the setting. Instead of being set in Tokyo like the first series, it's set in a coastal no-town in the middle of nowhere. Our heroines are the kind of country hicks who treat going to Tokyo as like visiting the moon. (This is very funny when they do eventually go there.) They include:
1. CHIKA, the orange-haired joyfully mental space case. It's all her idea. She was determined to start up a school idol group. It's hard to see her as heterosexual (e.g. looking up skirts, being energised and motivated by seeing gorgeous girls, glomping on to them and then not letting go even if she's glomped the wrong target). However sexuality doesn't seem to have become a conscious part of her yet, because she's devoting every breath and thought to her idol group. There's room for nothing else in her head. It's not that she's stupid, despite appearances (test scores, spelling mistakes, etc.) She can think about problems and she does notice things. However she's the kind of person who goes through life at 100mph, making you laugh with how enthusiastic she is.
She grows a lot as a leader, incidentally. She starts out like Tigger, along with some deeply weird thought processes (e.g. ep.6), but ends up having to face some realities as she thinks through the purpose and direction of her group, Aqours. ("Be like 'mu's" isn't good enough.)
2. YOSHIKO, the chuunibyou loon. Claims to be a fallen angel called Yohane who was cast out of heaven and cursed by God. Calls the other girls her "little demons". Interestingly, we learn in her focus episode (ep.5) that's she's actually aware of how cringeworthy she is and would like to become normal. That was a slightly scary episode when you were waiting for her to crash and burn, although it also ends up telling a positive, self-embracing story. (This franchise is good at that.)
3. MARI, the American-Italian-Japanese blonde. There are some mild hurdles with this girl. Firstly, she often talks in Engrish, although on the upside her voice actress makes it fairly convincing. Secondly, she's the school director, but also one of its students. This is... what? How can a pupil also be the school director? (What would happen if one of her employees needed to discipline her?) This boggles my imagination, but everyone in the anime seems to accept it because Mari's super-rich family has donated so much money to the school that they were apparently allowed to install her as its director.
4. HANAMARU, the temple girl. Loves books and is largely ignorant of technology, so is easily awed by it.
5. RIKO, the classical pianist who doesn't have time to join an idol group.
...and more, of course. The show starts with just Chika and her best friend, You. The school doesn't even want to let Chika start her new club. Good luck trying to stop her. They acquire more members. They're set impossible tasks. They might fail chaotically at the simplest of things, so for instance I laughed at their idea of a public broadcast in ep.3. They rehearse, although in hindsight there was actually a bit less of this than I'd expected. Idol shows are usually more focused than this on the day-to-day business of idolling, i.e. songwriting, dance practice, singing, etc.
It's a charming show. I was grateful for its absolute ban on showing the girls' underwear (although they cheat a bit with the swimsuits in ep.10). It's as lesbian-friendly as ever for this all-female franchise, but in a way that's gained it an LGBT fandom instead of just being button-pushing. (It's subtle enough that you'd have to be an experienced yuri-spotter to notice most of it.) Some fans have found it too similar to the original show, despite the very different backstory for the third years, but to be honest I wasn't that fussed. It's Love Live!. The original had been pretty generic too. It worked due to chemistry and charm, rather than anything particularly innovative in the writing (and Sunshine!! isn't trying to replicate the original's goofball secret weapon, Nico). It was a big international hit, but an unexpected one that no one saw coming. The original series has become a likeable blob in my memory and I'm sure this will become the same... but I'd still recommend it unreservedly and I'm looking forward to Season Two.