I've just seen it, and expected it to be good, with all the reference to my sassy girl but ended up being good at the begining and boring and confusing in the end.
I didn't like it much, I'd give it a 3 out of 10 stars.
The movie doesn't show nothing new, and I only liked the side story of it, from the e-mails.
I think if you understood the ending better, you would see that it did bring something new. It showed a man's love for a woman that was forgotten because of his memory loss disease. A new love took its place when he met the same woman again. I guess the message could be that if it is destined love, a simple loss of memory cannot take it away.
If you need clarification on the plotline, you can wiki this movie. Some devoted fan wrote a really long plot summary of it there, and I'm sure it will enlighten you on certain things.
In conclusion, don't give a movie bad reviews just because you don't understand it. :)