I enjoyed Bait, Jenkins' previous film so I had an idea of his odd dated style. Bait had a much more conventional narrative whereas Enys men is very layered, rhythmic and dream-like. Things like linear time and space are almost blurred occasionally. This film is highly symbolic in an almost Lynchian sense. It's unsettling in a psychological way and not in a traditional horror sense. The horror is from everyday tragedy and the haunted memories this creates.
The film is unfortunately rather boring because of the highly repetitive nature of the same person doing the same boring routine day after day. What this film lacks is stylishness and modernity. Jenkins seems obsessed with the ordinary and mundane. There are several close-ups of seagulls flying, waves crashing, woman making tea, reading a book, over and over again..... But if all you show in your films in the ordinary mundanity of life then your films will be feel that way to the viewer. Slowly more unsettling/bizarre elements are fragmented into this bland everyday existence but it doesn't break up the dull pacing.
At least after the end of the film me and my friend felt compelled to question what it all had meant. What was the point of this symbolic image or that one.
The main theme seems to be about complex unresolved grief. Grief that haunts us over and over. Survivor's guilt - what we should have done to save the person but didn't do. However, there is something more complicated than one person's grief being explored here. There is a whole Island's worth of historical grief but it is unclear how that relates to the main character in the film.
I couldn't say I would recommend this film. Maybe someone more familiar with the type of grief it was exploring would get something more out of it.