I feel a need to save this masterful summary from Behind the Nihon Review:

I can’t write a post about amnesia without mentioning ef – a tale of memories, arguably one of the most creative uses of amnesia as a plot device in anime. Unlike most examples in fiction which involve cases of retrograde amnesia, ef’s Chihiro suffers from anterograde amnesia. Her memories prior to a car accident are perfectly intact, as are those of her most recent thirteen hours, but everything else is lost, unless it is committed to a diary. Like most stories about amnesia, Chihiro and Renji’s subplot is filled with angst and uncertainty, firstly as Chihiro lives with the day to day difficulties of life without a working memory, and secondly as Renji endures the frustrating aspects of Chihiro’s disability on a longer timescale than she can even remember. What makes this story ultimately so powerful is the incredibly romantic way in which these two overcome Chihiro’s amnesia (“overcome” in the sense that they learn to deal with it, I mean). There’s a “love conquers all” aspect to the way their romance is resolved, but that’s because, especially for Chihiro, there’s something so irresistible and overwhelming about this love… it overpowers her amnesia and finds a way to survive and thrive, treating her disability as a trivial hurdle.

There were no dumb and poorly grounded comparisons with the Adam Sandler movie.