For me, currently, it is Cleopatra and Frankenstein by Coco Mellors. There is a lot of hate about this book. I don’t know why, the book for me is awesome. First few pages and I’m already hooked. Some chapters got me guessing on the relevance of it in the story but it all made sense at the end. Though it’s a debut novel by Mellors and some writing needs to be improved. Looking forward for her future books.
Eon by Greg Bear. One of the best exercises in sci-fi world-building I’ve ever come across. My buddy handed it to me and told me it was so good he had to take a break from science fiction for a while. I could see why!