Nick & Norah's Infinite Playlist is based upon the book written by Rachel Cohn and David Levithan. If you have read the book, you are aware that they made A LOT of changes to the story when adapting it to the big screen.
To me, the book focused more on Nick and Norah's developing relationship. We could hear their inner dialog as they worked through their feelings about their exes and began to realize there could be a future for the two of them. The secondary characters were just that...SECONDARY. The movie version gave their exes and friends a much larger part.
I found Nick's band mates to be very amusing in both the book and movie, but Norah's friend Caroline was beyond annoying in the movie. Yes...she did get drunk at the beginning of the book and need a ride home, but that is pretty much where her story ended. The movie drug her drunken antics out from start to finish. It was funny once, but by the end I was over it.
I thought they did a great job on the casting with the exception of Norah's ex, Tal. He came off as a total creeper to me. He was a player in the book, but once again the issue could be the fact that he kept reappearing in the movie. In the book, it was pretty much one scene and we were done with him.
Here is a link to the trailer.
Overall, I thought the movie was okay. They used a lot of the dialog from the book, which I enjoyed, but I wish they could have kept the movie a little closer to Cohn and Levithan's version of the story.