The biggest change for me was the scene at the vampire hotel. First, Raphael isn't in the movie at all. If you remember, in the book he meets them outside of the hotel and helps them get inside when he is pretending to just be a rando teenager. When he gets them inside that is when it is revealed that he is a vamp. He isn't even mentioned in the movie. Second, Simon doesn't get turned into a rat! He drinks the juice at Magnus Bane's party, but he doesn't turn. When Clary and the gang come to rescue him at the hotel, he is just tied up and suspended in the air, but there is no rat anything. I get why this was changed in the movie. It would be pretty hard to explain everything in the movie if it happened the way that it did in the book. So, I get it. I still wish it happened, but I get it.
My favorite character in the book and in the movie is Simon. I love love love Simon. He is so adorbs and I want to punch Clary in the face everytime she friendzones him. I also LOVE Magnus. The actor they picked for him is super hot and had me totes jealous of Alec.
All in all, I really really liked the movie. This series is so kick ass and I loved seeing it translated on screen. I'm sad that other movies won't be made, but hopefully other stuff will happen in the future (like the rumored possible TV show). I'm glad this is in my DVD collection and I can't wait to rewatch it!!