If you care about spoilers, don’t make the jump. And I will spoil both book and movie, so beware!
I have a tendency to get really negative when reviewing movies adapted from books, so I’ll start off with what I liked. I liked how the movie played up Harry’s self-sacrifice; the scene where he sits alone in the headmaster’s officer is very potent, and Radcliffe did a fine job with it. I much preferred how Harry made his entrance into Hogwarts, appearing boldly in the Great Hall and confronting Snape rather than randomly sending out the cruciatius curse at the Carrow sister. The scenes were epic, and on the whole I think the adaptation was well done, as I enjoyed seeing many of the scenes I had loved to read on the screen.
However, it’s the scenes they cut. There are three really important ones. One is Harry offering Voldemort a chance at remorse at the very last fight. The second is the discussion about Dumbledore’s past with Grindlewald, the Hallows, and his sister. The third is Snape calling Lily a Mudblood.
The first really loses us a characterization of Harry. Harry doesn’t just love the good guys, he genuinely cares about the others. It’s why he saves Malfoy from the fiendfyre in the Room of Requirement. After seeing Voldemort’s soul at the imaginary King’s Cross/purgatory place, Harry’s love naturally will move to try to help Voldemort. After all, Voldemort could not stand when Harry pitied his lonely state when Voldemort possessed Harry at the end of 5, and Harry’s offer to Voldemort for remorse, that show of love is more hateful to Voldemort than Harry’s fearlessness towards death or his desire to give everything for others. Harry’s not your typical action hero b/c his love is greater; losing that is not cool.
The second continues a botching that has been happening since Movie 3. A major but implicit theme in the novels are the new generation learning from the mistakes of the past and fixing them. While Peter Pettigrew was mocked and derided and powerless in the Marauders, Neville is loved and uplifted (this might bring up the question of why we never saw Wormtail die and what happened to that plot line in the movies, unless we’re buying that Dobby killed Wormtail in 7.1). While the Marauders hated Snape and attacked him mercilessly, Harry’s dislike for Draco doesn’t result in attacks on Draco (though suspicions abound), such that Harry can save him at the end (and Draco can return the favor in 7.1). A part of this theme was Harry’s rejection of Dumbledore’s temptations. While Dumbledore succumbed to the selfish desire to avoid responsibility and death and seek power, Harry does not and breaks (or loses in the book) the Elder Wand the Ressurection Stone. Harry’s virtue is more remarkable given Dumbledore’s vice, yet we never see that. Moreover, Dumbledore’s past combined with his secret knowledge of Harry’s need to die makes Dumbledore a kind of scumbag, so that when Harry names his son Albus Severus it’s a sign of Harry’s forgiveness towards their sins and failings, as both were prevented by their own weaknesses from truly helping Harry.
The last shows the tragedy of Snape’s situation. The movie makes it as if Snape lost Lily b/c James was rugged and cute, and Lily’s kinda shallow for liking James. The book makes it clear that Snape loses Lily because of his inability to get past his prejudice and hatred for Muggles born out of a hatred of his Muggle father, encapsulated not only by his choice to become a death eater but also by his outburst of prejudice towards Lily. Snape’s actions afterwards are very much a severe penance for his hatred.
There are other nitpicks (I didn’t mind Harry seeing Ron & Hermione on the way to the Forest, but if my best friend was about to give up his own life I may be a tad more upset, Ron). Like I said, the movie is worth watching a few times. But the movies are much better having read the books (I’d be confused otherwise), and unlike Peter Jackson’s Lord of the Rings, I expect that another adaptation of Potter will be in done in twenty years or so as there was much lost from page to screen.