I'll reference the first season but without spoilers. (The review has been updated after finishing the last episode)
If you are thinking about starting the first season, do it only if you want to get into the whole series. I think it's a good starting point. If you are planning to just watch the anime and move on, it'll probably not be worth it.
If you watched the first season and liked it, watch this too. It's more of the same but around 4 years later. There are also 3 episodes in a yokai alternate universe or something, I don't know what it was but it was good.
About the story and characters: most of the plot comes from long flashbacks which are basically content from drama CDs, but it's pretty good, at least for episodic anime standards. The 4 units take turns, and the last episode is the concert. It does a good job on introducing the units, the dynamics of their characters and their music. With 17 main characters, you can't expect much from each character individually, but the units as a whole have good dynamics. Like QUELL, Eichi and Shu are basically the mum and dad for the twins, I love them. 🤧
Animation-wise, there isn't a lot of movement, but the characters are well drawn. The 3D animation though? I think they blew out all the budget there. There's one for each opening and then another one for the last performance in the concert.
Sound-wise, I can't say much about the background soundtrack. But the insert songs, unlike in the first season or in Tsukiuta, there are a lot of them, and they work really well. Not to mention the new songs, OPs and EDs, they are really good. And so are the voice actors, with a nice mix of popular and experienced VAs and not so popular (but really underrated) ones. It's probably one of my fav casts for an idol series.
Conclusion: quite a mediocre idol anime, but I think it's a good starting point to my personally favourite idol series out there. There's a lot of quality and uniqueness in the music. There isn't anything like Growth or QUELL in other idol series. SOARA and SolidS aren't that unique, but nevertheless, amazing music. And the story in the drama CDs is pretty good too. SOARA even has 2 live action movies.
Let me say one more thing before leaving, in my opinion, there was a big gap in quality in the music between 2015 (the first year) and 2016. Just in case someone starts with the oldest songs and thinks I'm lying when I said the music is great. 👉👈
Thanks for reading! And I hope this caught someone's attention. I think Tsukipro is really underrated, at least outside of Japan.