Having just seen this a second time, it really pisses me off how much they changed/left out of the last 30 minutes of the movie.
Right from the start of the Hogwarts battle sequence it all turned into pure bullflax. For one thing, Harry did not make his entrance at Hogwarts the way it happened in the movie at all. What happened to the death eater brother and sister sequence in Hufflepuff which tied into the whole back story of the Gray Lady and how Voldemort had come to acquire the tiara thing from her? The way they portrayed all of this in the movie was just pure bullflax and at the end, for someone who didn't read the books. I can see it not making a whole lot of sense.
Another part that really bothered me was the Nevil sequence. This was a really EPIC moment for Nevil in the book and they totally ruined it in the movie. Why they changed this part is beyond me, cause there really was no reason to.
IMO they could have spent a few more minutes explaining Snape's story also. The fact that Snape really was a good guy the whole time because of his love for Harrys mother was poorly conveyed in the film.
Surprisingly the fact that Voldemort just disintegrates into thin air at the end of the film bothers me the least. Because of the way this sequence went in the books it would have been difficult to film it the way it really happened AND keep it exciting at the same time. So I can sympathize a bit here.
Meh, this is why books are ALWAYS better...