No game "requires" 3D, much how no game requires HD. However, some games are greatly improved by having it. 3D Land and Pilotwings are the best examples, but I keep the 3D on for most of my games because it helps provide a bit more information and makes the worlds a bit more pretty. Based on my experience...
3D is VERY Useful for:
*Super Mario 3D Land (The game is built around it)
*Pilotwings Resort (To the extent where I can't play flying games in 2D anymore)
*Kid Icarus: Uprising (Lots of Action and distances going on in air and on ground)
3D is SOMEWHAT Useful for
*Theatrhythm Final Fantasy (Helps notes stand out from colorful backgrounds)
*Resident Evil: Revelations (How far is that zombie-thing? Should I knife it? Will my >4 meter power boost work?)
3D is MILDLY Useful for
*Street Fighter 4 3D
*Kingdom Hears 3D
*Mario Kart 7
*Ghost Recon: Shadow Wars
3D is best turned off for
*Ocarina 3D (Gyroscope is more useful)







