Spectacular effects sunk by a predictable and cliched plot.

Rating: 4/10 (24 March 2019)

Arthur is the heir apparant to a subaquean dynasty ruling a society that is a smorgasbord of fustian and fantasy, despite being born to out of wedlock to a mother in exile from the feudal kingdom to which she belongs. Thus setting the standard of inconsistancy that permeates the plot throughout the movie.
Nicole Kidman, as "The Queen" (Should that be Princess if her father is still king?), does lift the movie out of the normal, bland, macho bravado dialogue and action that takes place as our hero battles his way from one perilous incident to the next. It's a pity she is dead, oh wait, now she isn't (inconsistant again).
Our hero is a (very) predictable impervious superman who can leap thousands of feet out of an airplane whithout a parachute, but struggles on a two-storey roof in Italy. Watch as he boldly goes where almost no subaquean half-human has gone before.
Borrowed from other genres? --
A submarine seizure (James Bond); Power Rangers; Sea Monsters (Godzilla and Lord of The Rings); Domesticated sea creatures (Finding Nemo) ...
Even Arthur himself is described as more or less as "The once and future king" - King Arthur of The Britons of the Round Table fame.
Nothing original is noticed here.