firehawk12
Subete no aware
Third and final, would be the cast. To be perfectly frank, I could not find it in myself to be attracted to Hotaro and Chitanda independently or as a unit. Hotaro felt entirely cliche to me, a stereotypical loner outcast disaffected youngster who just can't give a darn gosh dang it! The path of his growth I can comfortably admit, I suppose, inasmuch as it was "Hotaro slowly begins to open up and give a shit about solving these mysteries" but it wasn't anything new or engaging. It felt textbook. In fact, it was difficult to not see much of the show as the writers opening "High School Anime 101" and writing from there with plot points like hot springs trips and school wonders going on, but I digress.
I will say, the weakness of setting a Sherlock-esque character in Japan and more importantly, in high school, is that his flaws are just comparatively mundane. Oreki can't be an coke/heroine/drug addict or hooked on Vicodin because his leg is constantly in pain.
But his arc, up to the end of the film arc at least, is a deconstruction of his conceitedness. He "successfully" tricks Chitanda, then solves one of her big mysteries, and part of his reasons for wanting to expend less energy and disengage is because he feels it's a waste of his time. He's not necessarily disaffected, he is just bored. It takes his sister, through Irisu, to destroy that aspect of his character and allow him to grow into the character he becomes in the second half of the series.
You bring up Flowers of Evil at the end, but I think Kasuga and Oreki don't really have the same neurosis or share the same concerns and anxieties.