If you have a New 3DS or a New 3DS XL, eg the ones with the eye tracking cameras to keep the 3D effect in focus, it's super impressive with the 3D slider maxed. I heard the 3D is terrible on the old 3DS models though and is really hard to keep in focus. There were so few 3DS games that I thought used the 3D effect well. Off the top of my head the only other two I was really impressed by the 3D on were Zelda A Link Between Worlds and Mario Golf... or maybe Yoshi Golf? I forget. I got it free with my New 3DS XL because the pawn shop I bought from kept telling me as-is so I 'forgot' to mention they left the game I was testing the system on and bought the system as-is with the Mario Golf cartridge plugged in. Also got it cheap because they didn't know there was such a thing as a New 3DS XL and when I asked if it was a New 3DS XL they looked at me like I was idiot and told me no it's used.
Also saw it was on a pretty old firmware so knew it had been sitting in the shop half a year and used that info to haggle it down cheap too lol.