What I expected from Ondine was a mystical Irish folk tale, as the trailer suggests. It delivers in part, but ultimately debunks the more fantastical elements of the story that I rather liked. For me, this was disappointing, but maybe others will see it as an improvement.
The acting was decent in terms of the three leads, but between the mumbling Irish accents and low vocal audio level, I had to keep English subtitles on in order to follow. Some scenes were good, some scenes were bad, some were just unnecessary. Overall, I rate it as extremely average. I would rather that I rented it, instead of bought it.