The 3D effects were top notch, Disney/Pixar/Lucasfilm did a great job with the re-issue. Here's a brief synopsis taken from Wikipedia about how Disney 3D works:
Audiences viewing a film presented by Disney Digital 3D are given... circular polarized lenses... [which] allows much greater head movement than linear polarization without loss of 3-D effect or ghost images... The movie is projected digitally, ... at 144 frames per second. [...] Every 1/24th of a second ... the two scene views [right and left] are each shown 3 times [...] [T]he 72 image frames and 72 black frames fed to each eye in a given second should be perceived as a relatively flicker free image.
In front of the projector lens, an electronic device [...] inserts a polarizing screen that matches the polarization of either the right lens or left lens of the glasses worn by the audience. [...] The brain knits together the alternating left-right perspectives into a seamless 3-D view of the movie scene.