The story is one of the strongest points, but for you to understand this you need to watch the series from the right point of view. As a Slice of Life the story is about the characters, sure world building is important, but ultimately the story focuses on the 5 main protagonists, it makes you care about them, their lives and it gives a proper conclusion to them.
The art is pretty good for a studio with low budget like this one, at the start the CGI is noticeable, but after a while you learn to appreciate the backgrounds, the town and all the locations, you can see they put a lot of job on this.
The OST is a solid 10/10, with the composer of NieR is to be expected. From the Slice of Life to the action music every scene has a perfect ambience that lets you get immersed in the story. I doubt it's possible to find flaws about it.
The characters are the main motivation to watch the series and also get into the franchise if you're interested in the side material. You learn to appreciate them and you get really attached to them because everything is portrayed and developed around them, the support between the sisters, the romance between Yuuna and Tougou and the character development of the originally lonely tsundere girl is explained at the right pace and given the proper screen time. The fact that this anime (and the whole project) had 2 years of planning is noticeable.
The anime is really enjoyable by itself, but as someone who started watching it since the first week, I can say it's extremely recommendable to get into all the other material that is also part of this multimedia project, it contains multiple interesting information that makes you see the characters in a whole different light, and as I said the characters are the more important part of this franchise. The best way to do this is:
Watch the first 3 episodes of the anime, read the manga, watch episode 4, read the VN, watch episodes 5, 6, 7 then read the first 7 chapters of the LN, watch episode 8, read chapter 8 of the LN, watch episode 9, 10, 11, read chapter 9 of the LN and then watch the final episode.
The videogame is unrelated to the rest and it comes out until February anyway.
Overall the series delivers everything you want, good characters, writing, romance, action, interactions and it teaches you exactly what the title says: Yuuki Yuuna is a Hero. It teaches what is a Hero and how to be Hero, to you and the characters.
As a side note, even though I said the characters are the most important part it doesn't mean that the world is not interesting, on the contrary, the issue is that the anime doesn't give a lot of focus to it, only the necessary, that's why the speculation is also one of the best parts of this franchise, and this can be proved because it has been less than 2 days since the anime ended and there's already a lot of theories regarding the ending, and all of them are equally likely since this series is famous for leaving foreshadowing and references in all its media. I recommend you to watch it and join those theorists until those points are properly explained, and I know they will be properly explained because this series hasn't ended yet, it's only the beginning.
