Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is a fantasy/action movie about the half-human half-god Perseus, the son of the God Zeus, one of the earliest superheroes - thousands of years before Superman. The movie is a re-make of the 1981 movie with much of the same plot and characters which have little to do with the original Greek myths. Neither movie is great, but I like to see movies with Medusa, my favorite tragic character in the Greek myths - She was a beautiful woman who was vain about her hair then she was raped by a god, which made the god's wife so jealous that she turned Medusa's beautiful hair into snakes and made her ugly and toxic to all men. (You can tell the myths were invented by men because they usually get away with terrible behavior.) The special effects here are all CGI and much of the time it feels like you're watching a cartoon, but they're an improvement over the original movie with its animated clay and giant rubber monsters.
The story starts with Zeus threatening to destroy the city of Argos with an enormous monster called The Kraken unless the people of Argos sacrifice their princess, Andromeda, in ten days. So the clock is ticking as it always is in every action movie. Perseus and some other Argonauts embark on a journey to ask some blind witches how to kill the Kraken. They tell him the only way to kill the monster is to make it look into Medusa's face. One look into her eyes will turn any living creature into stone. Perseus decides to cut off her head and bring it to show the Kraken. Along the way he fights humans, giant scorpions, a demon from the underworld, and flying creatures from Hell, but the most important battles are with Medusa and the Kraken.
Perseus and his crew take a ferry across a river in the underworld to get to Medusa's temple. The Medusa we see there is not the Medusa we're used to seeing - a woman with snakes growing out of her head like hair. She's very much like the Medusa in the 1981 movie - a human woman on top with snakes growing out of her head like hair, two large fanged teeth, two large breasts under some kind of armored bra, scaly skin, arms with long clawed fingers, and a lower body that eventually becomes a long snake with a rattle and a stinger on the end, probably because they couldn't agree on which one to use so they used them both. We hear the rattle as she moves around, along with her devilish laughter. Her ruined temple in Hades is full of fire and lava and stone statues of the men who have tried to kill her. She shoots giant arrows and when someone looks at her face her eyes glow and she opens her mouth and shrieks, turning the person to stone.
She stones one guy, then whips her tail at it to destroy his stone statue. When Medusa tries to stone a non-human creature the Argonauts met along the way and he stays the same, she looks perplexed. After a long fight, Perseus uses his shield to look at Medusa's reflection so he won't turn to stone, and cuts off her head and throws it in a bag.
Perseus brings the head in a bag back to Argos on his flying horse, but he drops it and he and some flying demons play a fun game of chase the head in a bag. Meanwhile, Andromeda is hung from ropes over the ocean as Kraken bait, but at the last tick of that cliche action movie ticking clock, just as the Kraken jumps out of the water and is about to devour Andromeda, Perseus reclaims the bag from the flying demons, pulls out Medusa's head, which still has working eyeballs, and the Kraken turns to stone and crumbles into the ocean. This is hardly a spoiler since anyone who has ever watched a movie knew that it was going to happen from the very beginning.