I went to this with no expectations, as I vehemently disliked the first movie, which was a remake of the Ray Harryhausen classic. It's at least a decade since the end of the first fiasco and Perseus (Sam Worthington) is raising his ten-year-old son and living the life of a simple fisherman. His wife had died and that was a promise he made to her--to keep him from fighting. Because humans are no longer praying to the Greek Gods, they are losing their power. In Tartarus, Kronos, who is the leader of the Titans and the father of Zeus, Hades and Poseidon, is awakening and nothing will be able to stop him from wreaking havoc on the world. Zeus (Liam Neeson) visits his son Perseus and asks for his help--but it's not until monsters start appearing from the underworld that he agrees. But then it's too late. Zeus is betrayed by Hades and son Ares, who keep him prisoner and siphon off his power to feed the Titans. So Perseus, accompanied by Poseidon's son Agenor and Queen Andromeda, travels to the underworld to free his father.
As far as monsters, there is a chimaera, a trio of cyclops, some multi-torsoed/limbed warriors and of course the Godzilla-sized Kronos himself. Oh, and the black Pegasus that Perseus rides around on. One of the more interesting characters is Hephaestus (Bill Nighy, cast against type), who has lost his powers and talks to the robot Owl, Bubo as if it's a person (and in-joke to the first movie).
I found this sequel far better than the first movie, mostly because it didn't piss me off. There's not a lot of talk and it gets right to the point with the quest. There's lots of action, explosions and monsters.