It was surprisingly good! I think it's because of the wealth of visual detail; even with the third dimension removed, there was enough visual dazzle going on so that it still served as eye-candy in hi-def blu-ray. Dunno how it'd work on DVD or streaming; remove or blur the extreme detail and you'd probably remove the reason for this cgi-gasm of a movie to exist. Some of the scenes where 3d didn't fully work in the original movie actually looked better in 2d; brighter, and without that odd sensation of your eyes fighting each other to assemble an artificial and exaggerated third dimension. And some of the 2d scenes --- ones that in the 3d version had strong stereoptic effects --- look unusually flat in 2d. In one scene, for example, Jake and his blue babe were originally rendered in 3d, moving in the midground against a rock wall in the background. In 2D, it became obvious that the two visual planes were rendered separately and composited later; the rock wall was sharp and distinct, and showed high detail. The two rendered actors showed subtly different lighting and less overall detail; their original CGI processing had been spent in making them 3d. Remove the 3d, and their lack of detail and the lighting inconsistency (compared to the rest of the scene) stood out. But you had to be looking for stuff like that to notice it. There were no really glaring 3d/2d discontinuities. Sure, if you didn't like the original, the 2D version won't improve your opinion: the story's still formulaic, etc. But if you enjoyed the experience of the 3d version, the hi-def blu-ray 2d version is fun. Avatar holds up as a CGI tour de force.