This is a review by a manga reader that has been following Oshi no Ko in ongoing for quite some time, so I have a point of reference when it comes to comparing the quality; however I will be discussing only the period of 11 episodes or roughly 40 manga chapters, so there won't be any spoilers ahead. I'll be covering both positive and negative aspects of the series, and the final score is my SUBJECTIVE opinion - just because I didn't enjoy a certain part of the series, doesn't mean that you will as well.
The review only contains one spoiler, as I really needed to address the plot, but you were probably already aware of it anyway.

Length:11 episodes (1st one is 90 minutes long)
Watched in: Japanese and English

+Incredible songs in opening and ending by Ayase/YOASOBI and Queen Bee
+"Behind the curtains" take on the show business, that are based on the real events in Japanese industry
+Good voice acting in Japanese
+Some amazing visuals that came as a pleasant surprise
+Both Aqua, Kana and Akane are interesting characters, but

-They are put in this nonsensical teen melodrama that terminates the plot lines that actually matter(for now)
-The OST is on the weak side, with no memorable tracks (outside J-pop and OP/ED)
-Overuse of repeated animation
-Some poorly timed comedy that ruins the serious mood
-Drama's impact is weaker, in comparison to manga, due to rushed pacing

Oshi no Ko - spring anime of 2023 that had a popularity unlike any other. It's definitely been some time since a series went mainstream. After the release, it managed to hit an astonishing 9.35 rating on MAL - I don't remember the last time something like this has happened(I believe when Bleach got its new adaptation, it has also stolen the first place, but its rating wasn't that high). The popularity of OnK became a remarkable phenomenon, with some people claiming it as a masterpiece(I see you Gigguk) while others stated that it's an overhyped trash, that didn't live up to the hype. And this is exactly the core of the problem - Oshi no Ko became a victim of its own popularity. No work in the world will be able to satisfy everyone, no matter how well it is written.

The central theme of this anime is love, as the main character that the whole story revolves around, Ai Hoshino, struggles to understand this feeling, as she has never known love in her life. Because of that, she takes an opportunity to become an idol - hoping, that it would make her understand this feeling.
This is a good premise. It promises psychological conflict in the future, gives us an interesting theme, and sets up a lot of room for the future development. However, after the first episode, the gear shifts, which led to the all highest rating on MAL.
What would you do, if the love of your life was killed? Naturally, you would want revenge. Love and hared, being the different sides of one coin, shine in the eyes of Aqua and Ruby. They take different routes to carry the legacy of their mother, though both lay through the entertainment industry. Aka Akasaka combines high school characters, that he had made fortune creating before, with a Shakespearean revenge plot. And the result is surprisingly decent. Even though the romance plot line may be annoying to some, it isn't that relevant and serves more as a bait for a younger audience. This is perhaps the biggest issue one with this anime. However, if you are able to stomach that, or if that doesn't matter to you, the story is rather good, and, for the most part, will go uphill in the future.

Between choosing manga or anime, think about whether you like comedy or drama more. If drama is your cup of tea - then you should just pick the manga instead.

(very low - low - medium - high - very high)
ART: HIGH
Gorgeous eyes, beautiful colors, and amazing animation of performances. A pleasant surprise from Doga Kobo, but a welcome one. Too bad that it resorts to still images quite often. I hope that they can secure a bigger budget for next seasons. Also, cinematography could be much better
SOUND: HIGH
Good acting in Japanese, and not-so-good acting in English, which is quite a shame, as Kaguya's dub was awesome.
Great songs and weak OST
img49%(https://i.imgur.com/k1dzYo3.jpg) img49%(https://i.imgur.com/WZ9RuRh.jpg)
Story: HIGH
A boy sets on his quest for revenge to take down his father. While it may not be Code Geass (despite animated eyes) this is still well worth watching.

OVERALL QUALITY: HIGH
Recommended- unless you hate idols, teen romance elements and some inconsistencies. It's not perfect, but nothing is, so check it out, as next seasons might just bring something great. Or just read the manga, which is superior, though more demanding