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."