"Clash of the Titans" is loosely based on the Ray Harryhausen, stop motion effects film by the same name and even more loosely on Greek mythology. The Olympian gods are beginning to grow weak as humanity grow beyond their need for gods and stops worshiping them. Actually, one kingdom, Argos, is waging war on the gods by destroying their temples and statues, thereby weakening them by depriving them of human prayers. How they know this works is a mystery, but it does. Hades hatches a plan to scare humanity back into worshiping them by destroying the city of Argos, but he is really trying to destroy the other gods and rule for himself. Meanwhile, Perseus, son of Zeus, half god, half man, grows up knowing nothing of his true nature, loses his family to Hades, and broods throughout half of the movie. The other half he spends letting people die because he doesn't like his god half and refuses to use it until everyone else is dead and he absolutely has to. (Spoiled ingrate.) There are lots of amped up, CGI battle scenes, some for no reason whatsoever, Perseus has to be practically carried on most of the journey because he'd rather brood over his dead family and his origin than do anything about it, and Zeus gives Perseus all the help he could ever need despite the fact that Zeus doesn't know there is a plot against him and he, himself, ordered Argos to be destroyed, the very event Perseus (or the people dying around him) is trying to prevent. (Huh?)
There is absolutely no reason for this movie to exist except to show epic battle scenes between Perseus and various mythological creatures and the gods, and those scenes are all sadly less than epic due to Perseus' whining insistence to not unleash his inner god. The plot is full of holes and rushes along as it tries to get just enough story in to justify the next CGI, action sequence. Sam Worthington, as Perseus, is lifeless and bland. His character displays no emotion and he couldn't act his way out of a wet paper bag. The love story between Perseus and the other demi-god Io (wasn't it supposed to be the princess Andromeda?) is equally emotionless and must be spelled out for anyone to know it exists. They did eliminate the corny mechanical owl as comic relief, but replaced it with two awkward hunters who stumble over each other and, somehow, manage to not die. (The owl would have been preferable.) The music is reminiscent of every factory or conveyor belt scene from any Looney Tunes cartoon.1 There are a few attempts at morals for the story, like ruling with love is better than ruling with fear or it's better to be a man than a god, but these attempts to inject meaning or substance into the story are clumsy executed and quickly become tiresome.
I watched the 2-D version, so I can't intelligently comment on the 3-D elements, but no theaters in the intimidate area were showing the 3-D version, despite available screens, and I think I know why. I have read that the movie was originally not shot or rendered in 3-D, so it had to be converted, which lead to blurry action and odd, floating body parts.2 Whatever the case, I wouldn't recommend this movie in 2-D, much less paying extra for 3-D.