The first Expanse book and most elements of A Darkness in the Sky are fairly hard, but the later Expanse books and A Fire Upon the Deep, I wouldn't consider har

The first Expanse book and most elements of A Darkness in the Sky are fairly hard, but the later Expanse books and A Fire Upon the Deep, I wouldn't consider hard SciFi. That said, A Fire Upon the Deep is one of my favorite all time SciFi books and I'd highly recommend it.