Major Plot hole: The movie represents Hades as deeply hating his brother Zeus and as being banished to the Underworld by the same brother. Then how and why is Hades coming up on Earth to defend Zeus' statues being destroyed by humans?
Major Plothole: Why is Zeus helping out Perseus in his quest to destroy man's need for gods while it is explained that Gods needs human worship to survive? Was this a movie about the good effects of suicide? Because that creepy notion didn't cross our minds.
Major Plot hole: All gods have powers representing their own sphere of life on Earth. This is why Hades, the lord of the Underworld, is capable of releasing a huge sea-monster called the Kraken.....instead of Poseidon, the god of the sea.
Plot contrivance: King Acrisius witnessed his queen having sex with Zeus impersonating him. He was so furious that he ordered his wife's execution by leaving her in a coffin to drown in the sea....with the Demi-god baby. Which means that King Acrius decided to kill his former wife and Queen ONLY after she gave birth.
Plot contrivance: At the end of the movie, Zeus grants his son Perseus a reward: the resurrection of his newly found lover Io....instead of his whole family that was killed for no reason by Hades and created his first motivation to hate the Gods and work towards their demise in the first place.
Plot contrivance: In the final action sequence, a harpies steals Medusa's head from Perseus and instead of dropping it in the ocean, it keeps it in its claws and tries to fly away from Pegasus in the air.....with no real plan....until Pegasus reaches it so that Perseus can kill it.
Unaddressed Issue: Clash of the Titans is a movie representing the Greco-Roman mythology and legends. How can the Kraken, from Norse mythology, and Djinns, from Arabic mythology show up in this? We can thus infer that at least one research assistant showed-up drunk at the library.