Clash of the Titans is a fun movie - but to enjoy it, you'll have to turn off any understanding of the Greek gods and goddesses and sit back to enjoy the fast-paced story and special effects. But lets put the record straight on some of the biggest "innovations" in Greek myths found in the movie. There are more - but these are the most glaring ones.
Oops - Left the Titans on the Cutting Room Floor
The biggest "Oops" is that the Titans are not clashing in this movie. The Olympian gods and goddesses are not the Titans - those were their parents and predecessors. In the original "Clash", the enemy was Thetis, goddess of the sea, who was seemingly treated as one of the Titans, but she actually belongs to a still-earlier layer of Greek belief and may have been one of the nameless major Minoan goddesses who preceded the myths of Greece.
The core problem of all this "titan" talk is that the name itself has come to mean anything really big and powerful - like the ill-fated Titanic. In this way of thinking, the filmmakers (and most of the audience) just assume that all the gods qualify as "titans". Thus, "Clash of the Titans".
Perseus Is Not an Orphan
Bring back Mom. Perseus and his mother, Danae, were both saved from the floating box of death. Also, the fisherman who saved them was a prince whose brother ruled the country. His original name was Diktys - and while we can understand why the filmmakers may have wanted to change his moniker to avoid the audience sniggering, they couldn't come up with something more classical-sounding than Spiros?
Perseus also had nothing against being a king - which in the movie he seemingly equates with being a god. He is considered to be the founder of the Myceneans and to have been renowned as their ruler and king.
Who's That Girl and Where's Athena?
Athena may be an independent goddess, but she always has a weak spot for heroes. But the change in the storyline for Perseus requires that he is fighting the gods - not fighting alongside them. In the original myth, both Athena and Hermes assist Perseus. Io, though based on another suffering nymph-conquest of Zeus - is an addition for the movie - and possibly to make a sequel more enjoyable than the truth that Perseus and Andromeda married and proceeded to quietly rule Mycenae.
Andromeda Is Filing a Complaint
Of all the "mythtakes", the one involving Andromeda is probably the worst. In the original myth, she is indeed rescued by Perseus and they marry, go to Tiryns in Argos, found their own dynasty called the Perseidae, and have seven sons together - who become great rulers and kings. The original "Clash of the Titans" movie treated Andromeda with a little more respect.
By the way, her parents were the King and Queen of Ethiopia, not Argos. And her mother's boast compared her daughter to the sea-nymphs, the Nereids, who complained to Poseidon.
Zeus and Hades Don't Hate Each Other. And There's Another Brother!
Generally, in Greek mythology, Hades and Zeus get along reasonably well - which is why Zeus didn't interfere with Hades when he abducted Persephone, causing her mother Demeter to stop all plants from growing on the face of the earth until she was found and returned.
Also left out of the "Clash" equation - powerful sea god and lord of earthquakes Poseidon, who barely gets a footnote in the opening of the movie. If there had been a Kraken (see below), it would have fallen under his domain, not that of Hades.
Great beast! Bad mythology. The name of the Kraken comes out of Scandinavian myth, and while Greece had plenty of sea monsters, including one waiting to feed on the lovely Andromeda who was chained to a rock, they didn't have this one. The original was Cetus, from which the scientific name of "whale" is derived. Squid-like Scylla also qualifies as a more legitimately "Greek" sea monster.