Imagine watching a close up of an actor delivering a dramatic line... while the back part of his head or hair seems to float, disconnected from the rest of his head. Imagine watching a scene in 3D in which the "front" layer is utterly obviously separated from the "back" layer. 3D in which the visual depth that they've gone out of their way to tack on doesn't even stand out that much except to distract you by how obvious and tacked on it looks. The image above can only approximate how terrible it looks.
The idea to turn this into a 3D film was a last minute decision and the process was rushed - and boy does it come across on the screen. Unless you're easily impressed with 3D and haven't seen the likes of Avatar or Coraline, then I cannot recommend strongly enough that you skip the 3D version of Clash of the Titans and go watch it in standard 2D.
Hollywood has given us the filet mignon of 3D visuals with Avatar, which was shot in 3D using state of the art 3D cameras. So now that audiences are sold on the idea, Hollywood is now pulling a bait and switch by giving us a crappy McDonalds hamburger version for the same inflated ticket prices they charged for that filet. We've told you about all the 3D movies coming out over the next couple of years and how they're jacking up 3D ticket prices. If you want Hollywood to get away with offering a substandard experience at a premium price, then by all means, go watch these "slapped on" 3D versions of movies.
Minus the 3D, you'll probably find Clash of the Titans to be a fairly enjoyable action/adventure movie. Warning for parents: Some of the creatures in the film are VERY creepy for PG-13 and will probably be unsettling to younger children. For the 2D version I'd probably add a half star and give this 3 out of 5.