This would seem to play as straight-forward genre romance, with the sensibility of a novel of that genre, which I'll admit was not what I was looking for. It doesn't really have much of the "-com"(edy) element, irony or self-awareness or meta sensibility, that we're used to these days.
What I was able to watch before I had to switch off (and in giving it a second chance as I write) had a voice-over peppered-throughout, which unfortunately put what I considered poorly-written dialogue in these segments front and centre. One of my motivations for switching off was a line of dialogue that just sounded grammatically odd, it was an isolated example but underlined, for me, how I wasn't having a good time. The voice over narration is performed in a way that is more in the realm of a stereotypical upper-class British female, and is performed boringly, not unlike the voice of a Smart device, while a whole range of tones, accents and inflections of course exist here in contemporary Britain, so it's a shame that it employs an especially generic performance that has the potential to grate on the ear.
Elsewhere, It has some nice fantasy scenes, and some magical moments achieved within these, (it was stricking to see the main chacter trapped in a bottle by the beach - very effective) but never gets close to "Amelie", which seems to be a touchstone in terms of it's influences. Many will want there to be more to the light "mystery" and a grit to the potential dangers of getting obsessed with someone else's diary, as it encroaches one's real life, which I was hoping to get but it's a film that wants to stay rosy and in the middle ground. It's conversational and is constructed around 2-protagonist revelations as they talk, but we could ask for action to drive the story more.
Don't expect a romcom, but instead a romance, and not a Capital-M Mystery but touches of mystery, because that was the misconception me and my family went into this film with. Fantasy scenes are well done and are intriguing as an element that does succeed in holding the attention. Film should be supported and you should see if it's "your thing", it may well me, and you might love it.