I wish the director had stuck to the script 100 % (SPOILERS)
Although the completed movie is very similar to the script for the most part, there were some changes. Some were good, while some were not.
In the script the motivation of the antagonists wasn't explained like it was in the movie, and that change almost brought the movie down, although I understand, it was probably done in order to leave the door wide open for potential sequels (which probably aren't going to happen).
The script starts with the aftermath of the finale which implies that Kristy died (which later on turns out to be false) and then goes back 14 hours earlier. In the movie we see that the killers are part of some cult. Thankfully it wasn't explained in detail, because even like this, it was almost too much information. In horror movies, less is always more.
Aaron's death was much different in the script, and much better than what we got in the movie IMHO. In the script, he also comes back to the campus, but instead of going after the killer girl, he encounters Justine who's banged up, and before he can complete the sentence, he's shot in the head by one of the killers. It could have been the biggest jump scare in the movie, but alas...
The ending was also much different. In the script, Justine fights with the girl much longer. The fight is bloody and vicious. In the movie, it's over in seconds (basically, before the killer girl can even react), and because of that the ending lost a lot of impact.
I still like the finished product, but I think it could have been much more had those changes weren't implemented in the shooting script.