Despite its menacing 900+ pages, I couldn't put it down, in typical Murakami fashion. In the beginning, the characters seem weirdly selected, random individuals who's thoughts and behaviors aren't really explained much.
As time goes on (and a lot of time goes on), their motives, reasoning, and links are explained, yet there is still something that feels... off. While Aomame's character development is deep and well thought out, Tengo seems to be mindlessly put together, and I found him much harder to understand as a person - but maybe that's what Murakami intended. 
The third book may be slightly overdrawn, with the endless scenes of Aomame and Tengo doing virtually nothing just to keep the tension for the reader, leaving you feeling kind of frustrated and angsty. 
I've heard people complaining that the narrative spends too much time in the past, what happened before rather than what is happening now, but I actually enjoyed getting an insight into Aomame and Tengo's childhood, especially with Tengo's father. 
It's true that there are many mysteries that go unsolved, many character left veiled in a cloud of mystery, but overall, this really is a wonderful example of Murakami's master storytelling and his incredible ability to keep you hooked, even on characters that don't mean much.