I finished Harry Potter and the Half-Blood Prince around 2am Sunday morning, and immediately decided to re-read it. I'm clearly in Harry Potter (HP) obsessive mode because I've also now watched the 1st two HP movies.

Non-spoilery thoughts on Half-Blood Prince (HBP):

I really enjoyed the book, and am excited by how it sets everything up for the final book and the climactic showdown with Voldemort.

Some people I've talked to didn't enjoy it as much as the other books because there's less of a central mystery, instead it's focused on the flashbacks (which they didn't find that exciting). It might have been because I'd immersed myself in the HP universe by re-reading all the previous books but I was fascinated by the flashbacks. I really like how this novel pulls together a lot of stuff from previous books, which is a nice payoff for the reader. A co-worker pointed out that this book is less self-contained and more of a bridging novel filled with mythology (which makes sense since it's the penultimate book).

It certainly has some suspenseful and scary scenes, particularly in the final chapters. There is a character death which had me sobbing along with the characters during the funeral. HBP also answers some intriguing questions while introducing other very compelling questions (one revelation/action prompted my re-reading decision).

( Very spoilery thoughts on Half-Blood Prince ie. do not click on this unless you have already read the book )
Well, I'm ready for the next HP book already, but in the meantime I'm looking forward to the 4th movie!