From the perspective of a reader of the Harry Potter series the best part of the movie is when they explain the tale of the three brothers and the deathly hallows. In the book, this forms a somewhat difficult to comprehend yet crucial part of the story. The movie explains this very nicely.
Rupert Grint's acting is as awesome as in the previous movies. Rest of them play their part very well also. If anything could have been better would be the ending. The movie lacks a proper ending.