I cannot even talk about this without a spoiler tag:
Gah! The ending killed me (and Sam). Sam was a bitch, but I grew to like her. She made a ton of mistakes but I think by the end she had learned from them and if she had lived she would have continued being a better person. We don't know why or how she was able to replay her last day. That was one of the reasons I gave it a four.
One idea I had was that each day she went through could have created its own alternate universe.So in two universes, she died in the car crash. Juliet shot herself in another. She fought with her friends and stole her mom's credit card in the fourth. She spent two universes trying to save Juliet (one at home with her family) and she died saving Juliet in the final universe. But her story continued in the universes where she lived and those events did happen.
I realize that probably wasn't what happened, but I like the idea. I did love on the final day the issue with swimmer that they made late and how Sam tried to negate it by stopping at Starbucks and it completely backfired. I thought it was funny.