If your holiday reading manifesto is 'I want to feel everything intensely and I have no shame about it,' these are your books. Maximum spice, full immersion, zero regrets.
Haunting Adeline by H.D. Carlton is intense and dark, with a paranormal mystery layered underneath the romance. The spice level is genuinely high. The psychological tension is constant. This book doesn't ask you to like what's happening on the page so much as compel you through it. It's not for everyone, but if you're looking for a reading experience that shakes you, this delivers.
Ice Planet Barbarians by Ruby Dixon starts a series that's built on pure, unapologetic spice with the softest hearts underneath. Blue aliens on an ice planet, human women crash-landing, forced proximity romance. The worldbuilding is weirdly solid for books that are primarily about intense intimacy. The first book especially is less plot, more heat. It's indulgent and doesn't pretend otherwise. Gild by Raven Kennedy is a fantasy retelling of King Midas with a protagonist locked in a tower as his kept woman. The spice level is high. The power dynamics are complicated and intentional. The story is told in a way that makes you lean into the tension rather than resist it. By the end, you'll need book two to process what you just read. And Zodiac Academy by Caroline Peckham and Susanne Valenti is paranormal romance with a massive spice level and a lot of plot underneath it. Twins discover they have supernatural powers, get thrown into a paranormal academy, and immediately find themselves in the center of complicated group dynamics and romance. It's long, it's immersive, and it doesn't let up.