I'm a little late to the party myself, but it seems like there's been a pretty healthy discussion. A couple of thoughts, in no order whatsoever:

Spoilers, ahoy!

(1) I was impressed with how Eddie (and I suppose, how King handled Eddie) dealing with the possibility that he was going to lose Susannah. He is now, after all, a gunslinger, and he realizes there are larger stakes here than how he feels about Susannah. Just as Roland had to sacrifice his gunslinger brothers one after another, Eddie would do the same to Susannah for the Dark Tower. I'm not commending him for not pulling his hair out and running around screaming, I'm just satisfied that King didn't spend half the book dwelling on Eddie moping around and going nuts or threatening to kill Roland or something.

(2) Hindsight is 20/20 and all that, but I've seen where the Dark Tower is headed for about, oh, ten years now. No leaps of deduction on my part: I read somewhere--don't remember where--that the King short story Umley's Last Case (a story in which a fictional detective meets his writer/creator) will play a role/have an influence on The Dark Tower.

My theory is that before this is all over, many if not all of King's major characters events and possibly even settings will find their way to the Tower and allow King to give them all closure once and for all. He is, after all, retiring. Would I like to see an ending like that? NO. But I think it's what awaits Roland, Eddie, Susannah, Jake and Oy at the top of the Tower. (Many fans point to the name Crimson King as evidence that King "himself" will be a character by the end of the Tower series.)

(3) Dr. Doom?! Dr. freakin' Doom?! Oh, come on.

(4) I'm curious to see how Dark Tower-related characters will finally play a role in the quest for the Tower: Roland remembers having met characters from Eyes of the Dragon, although we've never heard the entire story. Ted Brautigan(?), the "Breaker" from Hearts in Atlantis is tied directly to the Tower, but whether we'll ever see him again remains a mystery. The little boy in Insomnia is, to paraphase, supposed to intervene at a crucial moment to save the lives of Roland and Eddie. And finally, I think we will see Jack Sawyer (The Talisman, Black House) before it's all over.

(5) Nitpicky, geeky fanboy observation: Has anyone noticed that we've met Roland's "Twinners" (to use the term from The Talisman). Twinners in alternate worlds feel everything their doubles feel, cutting across time and space. I don't remember all the names, but characters in both Dreamcatcher and Black House lose the same two fingers that Roland lost in The Drawing of the Three. Coincidence? I think not.