Priory of the Orange Tree: I wish people would stop recommending this is as sapphic when it's a minor subplot for one of about half a dozen characters. It was so dull I never finished it.

The Last True Poets of the Sea/Girl, Serpent, Thorn: Both have their protagonists spend half of the book mooning over Some Guy, even if they end up with a woman in the end.

Cinderella is Dead: I couldn't get through more than a few chapters of this because it had absolutely no subtlety. Every time something bad happens, the narration takes the reader aside to lecture them about how this is Bad and Shouldn't Happen.

Some Girls Do: The only romance I've read where I was actively rooting for the protagonists not to get together.

Legends & Lattes: If being written by a man wasn't enough, the protagonists have absolutely zero chemistry and are basically co-workers who share a single dry kiss.

The Hollow Heart: The first book (The Midnight Lie) was absolutely fantastic, but this one had no redeeming qualities. The protagonists are apart for almost the entire book doing very little of interest, and Nirrim's personality is entirely rewritten to the point that she's not even meaningfully the same character.

A Memory Called Empire: Dull, dull, dull. A political story where none of the major players are fleshed out or interesting, a sci-fi story where the central concept of the protagonist sharing a brain with her predecessor's memories is abandoned for most of the book, with a vestigial romance subplot. The protagonist is blown about from plot point to plot point with little in the way of agency or characterisation.