The Dark Tower VI: Song of Susannah (2004) by Stephen King
Ok, after Wolves of the Calla, almost anything was going to be a kind of letdown. I mean, Wolves was kickin'.
Song of Susannah, though, moves the plot forward significantly, since here is where Susannah/Mia/Odetta/Detta finally has her/their(??) baby. Ok, that doesn't happen until the end, but this novel explains exactly who/what the baby is. We also learn more about the Rose, the vacant lot, and why Calvin Tower has refused to sell it to Eddie's former bosses.
The most fantastic part of this book, though, is when Roland and Eddie run into Stephen King himself. I mean, just listening to this part made me dizzy, with all that meta-ness flying around. It's as if King is working through his complicated relationship with the Dark Tower story by imagining a scenario in which its characters confront him when he was about to abandon it (it started off as a fragment of The Gunslinger and was then tossed into the garage).
In imagining himself interacting with Roland and Eddie, King is not just giving them another dimension; he is fictionalizing himself, creating a narrative of a narrative. It's only fitting perhaps, since the entire series is about multiple dimensions/universes. The Dark Tower stands at the center of it all, and King is inviting us to think about our own universe as just one of many. This reminds me of the Polish SF novel Nest of Worlds, where characters would read about other characters, and in turn were read about by still other characters (yeah, time for some advil because headache).
Looking forward to Dark Tower VII: The Dark Tower. And there's another book, too, yes? The Wind Through the Keyhole, which actually takes place between IV and V. Off I go!