The male and female lead characters are played with exactly the right kind of subtlety. But as is often the case with comedies, the supporting characters are essential for the humour - although "supporting" may be a misleading term here, as the two characters in question have probably more screen time and more lines than the two protagonists. Veteran actress Anita Wall delivers a superb performance as the grandmother. And Erik Lundqvist gives an outstanding debut for a boy his age. The performance of these two alone would be enough reason to go an see this film.
Two minor points of criticism: The developing love story is hindered a bit by the fact that we see little character development in the female lead. That was certainly intended, as she is definitely an Asperger's case. Still, some scenes between her and her male counterpart could have been a minute or two longer, so that the audience can better get into the relationship they are meant to root for. Then there is the problem of two rather strong but underused minor characters. Elin Petersdottir and Lia Boysen do an excellent job, but their characters are unsatisfyingly presented by the script. If you have two female characters in the film who are presented as that strong and forceful, you should use them more and tell us more about them. If you do not have the time and/or inclination to do that, do not present them as that potent a factor in the film.
An almost perfect film - I'll give Hemma 7 out of 10, easily, probably even 8 out of 10.
I've just seen this film at the International Film Festival Mannheim-Heidelberg, and talking about the audience reaction, the general mood of the crowd was at least of a "8-out-of-10"-quality....