Before anything else, the plot seemed quite unique. Whoever heard of a person who forgets about nothing BUT their friends after a week has passed?
At a glance, the series might just be passed off as a typical 'problem solving' type whereby the aim of the entire series is to find out what this 'huge, mysterious' problem is caused by and solve it.
The characters are the added romantic comedy theme is what made me really appreciate this series as something much more complex and profound. The simplicity and neatness of the animation, combined with the soft tones of the background music, draws out and continually sustains a very gentle, mellow tone throughout the series. Furthermore, it also subtly directs the readers attention towards the characters themselves.
As for the characters, I guess what I really liked was how unique they were. Amongst the character cast, there wasn't a clear way to distinguish and label characters based on roles such as 'the one for comic relief' or the 'serious one' because they were all just so human. I like that- it's nice to see the producers pay so much attention to every single one of the characters well-developed, feeling and multifaceted. If we were to be nit-picky, I could say that there were a few supporting characters whose personality was not developed at all. However in my personal view, I saw these supporting characters as a very natural device used by the producers to help encourage character development for particular characters.
It's a very uplifting anime to watch.