I'm a huge Potter fan, and having pretty much memorized the plot details of each book (yea, I've read them all quite a few more times than just once
), I can say that this movie can be enjoyed to a much greater extent if you've read the book and can suspend your disbelief, and let your imagination fill in the missing plot pieces - after all, they are all there, just not shown in the movie!
I thoroughly enjoyed it, but at the same time did notice plenty of missing or oversimplified parts, which did not bother me at all. The special effects were top-notch, and the new Dumbledore is perfect. I can't wait for the DVD!
PS: For those who never read PoA - I consider this THE BEST Potter book out there, so use this opportunity to start reading