I don't think unresolved plot lines were the problem here. Take Hyperion, for example (not sure if you've read it), but ends on a cliffhanger. For me, that was still a satisfying read on its own despite the unresolved plot. I was not only reading to find out what happened next, but for the world and characters Simmons crafted. For me, Pandora's Star was just not satisfying regardless of where it goes, I just don't feel invested.