Spock Must Die! was rather weird, in its challenge to transporter technology, its assumption that Organians could be contained, and its complete removal of Klingons from the picture.
Mission to Horatius was a tad weird, in that it was a youth-audience novel before any adult-audience ST novels were published, and in the fact that the draft that was first submitted for approval had stuff in it that was considered offensive even at the time, and that it had issues that survived into the published version.
Almost anything Marshak & Culbreath wrote was inherently weird (and often harder to follow than the parts of How Much For Just the Planet that were intentionally hard to follow).