I'm definitely in the minority when it comes to this one but I just didn't find myself enjoying it that much. It was interesting to get a glimpse of Rebecca's life before she disappeared but I don't feel connected enough to her to really care about her story.
If you've read If I Were You you'll see that Rebecca and Sara are pretty much the same character. I just find it impossible to believe that the person who randomly finds Rebecca's journals has exactly the same tastes, education and dreams for the future as she did. I also can't understand why both of them are so attracted to Mark - he really is a complete and utter douche and I can't stand him.
I think for what it is this story is completely overpriced, it's currently £1.99 on kindle and is only about 40 pages long. I'm assuming you have to read all four of the short stories in Rebecca's journal to get any kind of resolution to the story because this one certainly doesn't add anything new to the series on it's own.
I don't think I'll be reading any more of Rebecca's Lost Journals. I'd rather save my money for something I know I'm going to enjoy. I haven't made up my mind about continuing with the Inside Out Trilogy though, I already have the next 2 books so I might give them a try at some point but I'm not going to be in any rush to do so - I'm starting to come to the conclusion that this series and I just aren't meant to be.