Long time lurker, first time poster.
I will say, unashamed, that I'm a huge fan of these books. They're cheesy at times, but they're some of the better YA vampires books out there. I was sad when they decided to do a movie because they were just trying to cash in on the Twilight/Hunger Games craze. Plot-wise, there are many things that affect the first book/movie that are explained in later books. What Lissa's powers are and mean, what happened in the accident, a lot of motivations, etc. They just took the first book, added bits from the second and third (nothing good), and made this.
After all was said and done, only two things really upset me: the accents and the ending. There was no reason for the British accents. They are all American in the book. There are moroi and dhampirs from other countries that show up later. I'm guessing it was just some way to distinguish between the two groups, as though fangs wouldn't do that? The final speech never happened. I PAID to watch this in the theater with my friend. We were willing to accept everything until that ending. It felt like their way to wrap it all up, knowing they would not be making another movie.
I also paid for the bluray with a digital copy, bought & read the sequel series, have the three graphic novels, and even bought merch.