I just finished IM
To be honest it took me a while to get into it because the characters were so empty and hateful. But as it went on it was like a celebration of the cold and shallowness people can exhibit when they have little else going for them other than their looks.
The ending is by far one of the best twists I've ever read and I went away from the book with a change of heart and an even greater respect for Chuck and his writings.
I still like Haunted the best though.