In spite of its very low 19% rating on Rotten Tomatoes, I watched it because of the lead cast, namely James McAvoy and Alicia Vikander. It's indeed not a great movie, but I didn't feel it deserved such animosity. It's just a plain, "meh", movie. A man and a woman meet during holidays in some sort of vacation village at the French Atlantic coast. He's an agent from the MI6 and she's a oceanographer (he presents himself under the cover of another job). They each take a few days off before an important mission; for him to go obtain intelligence about an IS leader in Africa and her to dive in a deep-sea submarine to find about life at the bottom of the ocean. They fall in love and promise that they'll see each other again. As she engages into the sea, he is taken prisoner, and somehow... (insert some sort of mystical, spiritual stuff). Well, the movie doesn't quite deliver on the spiritual part; the two story-lines just have really nothing in common.
I didn't really mind this lack of overall consistency. There is the first part which is the long, full-fledged love arc in the vacation village. There are some cheesy dialogues and mood music that are reminiscent of weekdays afternoon TV movies but the important cast and the thematic around their characters' jobs (MI6 agent an oceanographer) gave me enough goodwill to care and find some sort of chemistry in their relationship. The second part alternates between him being a prisoner of IS and her going to her day-to-day oceanographic research (before the final dive). Again, it's quite superficial and nothing really stands out, but it's followable. There are nice shots of the sea and of the submarine.
On the technical side the sound mixing was bad and it was hard to understand the dialogues over the background sounds. Some of the framing was awkward, again evocative of TV movies. I watched it without minding, and went on with my life. I've seen way worse and endured way more boredom in films that are considered way better.