I wouldn't say 3D is "needed", but there are those isometric rooms specifically designed to screw with people not using 3D.
My thoughts on the game: Remember when NSMB came out using SMB as its touchstone for items and music and everyone said now they should make NSMB based on the other 2D games? Well this is NSMB3, straight-up.
Also I died a lot on this one level so it gave me infinite invincibility and I felt bad.
Also LOL at the second Star Coin in 5-2.
Is anyone using that alternate 3D mode?