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Went to this last night. Only $1 extra for the 3D. Which is cheap since I read on message boards that people had to pay $2-$4 extra.
Anyway, the movie didn't really have a plot. Three people somehow fall into the center of the earth, and spend a half hour or so trying to get out. The 3D could've been used WAY more. This was my first 3D experience, and I felt they coulda used the 3D more instead of hitting us in the face with yo-yo's and spitting water in our face.
If you want a trip, and the 3D isn't too much extra, I would recommend checking this out. Otherwise, I probably would've enjoyed the film the same if it were 2D.
I hope Final Destination 4 uses it's 3D better.