As someone who read (most) of the original visual novel it was based on and wasn't a huge fan... this anime adaptation of Daitoshokan no Hitsujikai was... mildly better, but barely?

Anime adaptations of visual novels (and well adaptations of anything) tend to mostly be used for advertising the original visual novel, and at least for me this anime was mostly better for one thing: actual good pacing. (if a bit fast at times)

The main problems I had with the visual novel were that it too slow paced, even for a slice of life heavy visual novel, AND most of the characters were boring. I could take maybe one of these issues if a VN eventually gets good but having both made the original VN a struggle.

Thankfully the anime had the decency to skim past a lot of the cringe stuff of the original visual novel like forcing the MC to crossdress multiple times, Nagis obnoxious humor, and Ureshino's dumb "femdom loli" tendencies.

The anime also competently gets the main characters' personalities down well and adapts SOME of their backstory melodrama into the plot. They at least introduce the library clubs goals, introduces the Shepard magic, and has a clear beginning, middle, and end and ties up things well for a 12 episode anime. One of the big flaws I had with the original visual novel was how long it took to even introduce the Shepard "magic", especially since you had to finish a side route to see more.

However, despite the improvements the anime made, they can't fix a lot of issues I just have with Daitoshokan as a story no matter the medium. As said earlier, I think the characters are mostly forgettable archetypes. Most are at least not bad (outside Nagi who I find more annoying more often than not), and at least have kinda interesting backstories, but I just don't care much due to their incredibly basic personalities. The only character I legit like was Kanasuke (which thankfully seems to be the majority opinion). She is very goofy and has by far the most interesting backstory. The anime may make it seem like the characters' backstories were rushed but honestly... they were also THAT short in the original.

I think the story in general would just be better if it focused much on these character focused backstories instead of a mediocre mix of those plus this Shepard magic plot that had a really boring pay off, both in the VN AND Anime. Instead we got a half-assed mix of both along with mostly mediocre characters. If it weren't for the anime's fast pacing, I would likely have dropped the anime.

However, one big flaw with the anime specifically... is the weird way they implemented the harem romance. In the original visual novel, there were proper buildup about how the main girls have feelings for the main characters but only get their dramatic romantic payoff in their respective routes. In the anime? It implements A LOT of these romantic payoff scenes including multiple kissing scenes but the main character Kakei never really 100% chooses a girl by the end. The anime mildly prefers Tsugumi, but there's so many scenes where I'd be like "wait but she kissed him but now there's romantic tension with this other girl now?". Sadly this flaw is partially due to the visual novel's structure and the animations clearly trying to keep the spirit of it, but imo they should have just went all in on the Tsugumi romance ending since the animator's clearly preferred her.

Overall, the anime adaptation of this story is watchable, but it can't really fix many of the flaws I had with the original outside pacing. It's still a mediocre mix of slice of life melodrama with a mediocre execution of magic related to memories and seeing the future.