Early reviews on the film have been resoundingly positively so far.  General consensus is that, like the book itself, Half-Blood is a slower, more deliberate entry in the film series -- more character and exposition driven, and a superb build-up to The Deathly Hallows.  Most concur that Yates has a better handle on the material over his first attempt with Phoenix, perhaps due in part to a more generous running time and the return of screenwriter Steve Kloves.  Says IGN's Chris Tilly: "This is the first Potter flick that functions as a fully working thriller."

I like Drew McWeeny's review.  Some choice quotes:

"This is absolutely the best of the "Harry Potter" films so far.  That may sound like faint praise, but it's not.  Even removed from the sliding scale of this particular series, "Harry Potter And The Half-Blood Prince" is a remarkable fantasy adventure, dense and serious and adult, and it serves as a fascinating benchmark for just how far this series has come since 2001.  I've always liked the ambition more than the execution, but now, finally, it feels to me like we're seeing the full potential of the series realized, and the result is somewhat breathtaking."

"But in spirit, this is the first time I've felt like I can wholeheartedly recommend this to anyone as a great film, not just a great entry in this particular series.  That's surprising considering how far down the road we are, and I sincerely look forward to seeing this one again as soon as possible."

The movie is excellent, my second favorite after Azkaban.

I have a few quibbles with some of the choices they made in the adaption but that's all they are. Quibbles. This is the first film since Azkaban that hasn't felt rushed. I'll admit it isn't especially plot-heavy but that leaves room for some tasty character development (and a surprising amount of humor. This is probably the funniest of the films).

The look of the film deserves special note (and the cinematography should get an Oscar nod). The castle has never looked so beautiful... and yet so foreboding. Definitely a far cry from the Sorcerer's Stone days.

I saw the movie myself last thursday, my first IMAX experience, and although I agree with you that it's definitely one of the best, I thought there was a surprising LACK of humor this time round. It was pretty serious throughout, and the comedy that WAS there wasn't particularly good.
I remember the 4th and 5th as being more enjoyable in that respect.

Also, to me, it STILL felt rushed, like all the other movies, but I have come to accept this.
The books are quite long so this is probably a necessary evil.

It would have been nice if they had spent a bit more time on developing Tom Riddle's character, like the book, and two of the most dramatic moments in the story, Dumbledore drinking the strange liquid, and Dumbledore getting killed by Snape are over surprisingly quick.
Especially the first of these two would have hit home far more if it had been drawn out a little, but maybe that's just me.

Still, definitely one of the best so far.

Oh, and Snape is awesome, as always. Alan Rickman FTFW.

Saw it Wednesday night.  Very good, IMO.  Most importantly, this movie actually moves at an easy pace and spends most of its energy on character development.  After the last three blazed through scenes, it was nice to slow down and enjoy the relationships among the characters for a change.  It would have been nice if they hadn't cut out so much of the Tom Riddle backstory, but in the context of the films, I can understand why they did.  My only real complaint is that the final scenes were over way too fast and as a result, fell flat.

After being extremely disappointed with Yates' work on the fifth film, I'm glad to see he's shown remarkable improvement on this one, and I'm optimistic for how we will handle the next two.  That said, his big weakness seems to be with action scenes, and since the eighth film will have some pretty major action scenes, I hope he gets some good help for it.

Concerning Hooper's score, he's still far and away the weakest of the HP composers, but he did a better job than in the last one, so at least he showed some ability to improve.

In Yates' defense, he hasn't really been given the chance to direct a full-blown action scene. Most of them have been over in two or three minutes. But yeah, he'll have to really step up to the plate for the big scenes in the seventh book.

(I did enjoy the Dumbledore/Voldemort duel in the fifth movie.)

I've noticed that people have been split on the humor. I dunno. I personally thought Ron on the love potion was hysterical (followed by Harry feeling lucky). I was also in a theater filled with people who were very receptive to these moments.

Hooper's score was functional. He adequately covered the emotions necessarily but the music itself doesn't have much identity or thought put into it. The only scene I thought he really bungled was Dumbledore's last. I also noticed some music from the fifth movie was tracked in.

Rumor has it that John Williams has been approached to score the last two movies. It all depends on his schedule, so I hear. This would obviously be ideal.

I'll have a formal write-up sometime in the future, but I thought this was a tremendously satisfying film.

Still gonna have to give the nod to Goblet as my favorite, but Half Blood certainly finishes a close second alongside Azkaban.

Agreed.  Since reading how lauded cinematographist Bruno Delbonnel is, I was paying particular attention to how the movie was shot.  It's masterful, to say the least.

Much of the humor stems from the teen romance angle, which can be a take it or leave it sort of thing for many.  Personally, I thought the kids did a terrific job emoting the proper balance of nuance acting in this one; the furtive glances, the uncomfortable reactions, and the remarks laced with subtle sexual innuendo.  Though to me, nothing comes close to genuine hilarity than the Moaning Myrtle bathtub sequence in Goblet of Fire. :p 

On the opposite side of the coin, Half Blood does feature one of the most emotionally-charged scenes I've seen in the film series yet -- and that's when Harry consoles Hermione out in the corridor.  Watson was tragically wonderful here.

I did mention it in passing prior, but yes, getting Williams back would be a real coup for the finale of the series.  The question is, how would he approach it?  Would he choose to continue off of the thematic material he introduced in the first three films?  Would he adapt any pieces contributed by Doyle and Hooper?  He'd be in a most intriguing musical position, to be sure.

My favorite shot is right after the Hermione crying scene, where the camera zooms out to the tower they're in, crawls up it and centers on Draco Malfoy brooding on the top of another tower. Gorgeous. This will definitely be a Blu-ray purchase.

Yates seems to have great taste in cinematographers. He grabbed Eduardo Serra for the Deathly Hallows films. He's best known for his stunning work in Girl With a Pearl Earring.

Definitely lots of awkwardness. A lot of the laughs for me came from Lavender Brown. Jessie Cave was hysterical in the part.

Hard to say. He certainly has a bunch of themes he can work with. From Doyle, there's the Harry theme as well as the creepy ascending Voldemort theme (although Williams is more likely to use his own, from Sorcerer's Stone). Depending on whether Umbridge appears in the next film, her theme could make a cameo. Just depends on how interested in continuity Williams is.

Aside from Hedwig's Theme (and mostly just the A part of the theme), neither Doyle or Hooper were especially interested in working with Williams' material.

The Half-Blood Prince is out on home release this week, but more importantly is that the Blu-ray edition houses the first teaser trailer for The Deathly Hallows:

http://www.youtube.com/watch?v=PAAYsGJnh60

Higher quality versions will likely become available soon.