I'm starting my medicine rotation in a few months but I want to read a textbook that could give me a decent insight on the pathophysiology, diagnosis and treatment of diseases. Harrison is just too long.
second this. step up is really good. they also put a bunch of landmark studies to know about in the "quick hits" in the margins which are great for pimp questions.
If you are looking more for textbook rather than review book, you could try Cecil's Essentials of Medicine. Still long (~1200 pages), but it's a pretty solid book.