We saw HARRY POTTER AND THE HALF-BLOOD PRINCE last night at the Century City AMC Imax theater. The writer and director did an impressive job of making an enjoyable movie -- indeed, one of the best-looking of the Potter series -- out of a story that is basically a second act intended to set the stage for the final book (which will be split into two movies). Much of the credit goes to Steve Kloves, the screenwriter for all the Potter movies except the previous one. Kloves excels at cramming lots of story into the screenplay, while also allowing time for character moments and set pieces that look great.
One criticism: The movie had one of the most pointless uses of 3-D technology I've seen. The previous film had a climactic battle in 3-D, which was fine; the audience got worked up waiting for it. Here, the opening sequence was in 3-D -- and nothing else in the movie was. So the audience was left with the enormous 3-D glasses sitting in their laps (or on their heads, if they wanted headaches) useless.
The filmmakers are also dealing with an unavoidable complication that arises when adapting the late chapters in a multi-character epic: Gobs of characters have walks-ons. Here, Timothy Spall has about 30 seconds as Peter Pettigrew/Wormtail, which I imagine was at least a day for the actor (particularly with his silver-hand prosthetic). The writer can add a character to a scene with a few strokes of the keyboard; but it's quite another thing for the producers to corral the actor from a previous movie and haul him or her onto the set for a few seconds of looking sheepish.