I never used a case on a phone and never had a problem. Why buy a slim, light state of the art phone just to slap a case on top of it? Not saying i like the kind of flashiness this phone is offering though.
In the Nintendo 3DS the 3D felt great, specially in the second iteration with the cameras that auto adjust the 3D effect based on your eyes position. Outside of gaming I can’t see any practical use. 3D movies always felt weird to me.