Laura, my wife, and I went to see this on Easter, caught the earliest show which was nice and uncrowded.
Clash of the Titans begins with a potted history, which totally screws up the Greek creation myth and the conflict between the gods and the titans. The coherence of the story does not get any better from then on. The special effects are quite good, the action is above average and the movie looks good but the plot is weak, contradictory and does constant violence to the fabric and ideals of Greek myth. If you can let the plot wash over you in a Zen-like state to enjoy the action scenes and the pretty visuals, you will be better off for it.
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More spoiler laden comments follow after the break.