Shovel Knight

Yacht Club have made a truly excellent game with Shovel Knight. Not only are the core platforming and combat mechanics carefully crafted for a balanced and challenging experience.
But the thing that really did it for me was how well Yacht Club weaved storytelling as well as intuitive but invisible tutorials directly into the gameplay that not only evokes the creativity of nostalgic games, but reminds us only of the best parts of them.

None of this is particularly new though (Mark Brown has covered this extensively in his Game Maker's Toolkit video on the exact subject), so don't just take my word for it.

As a 3DS port (okay I played it on a 2DS) the bottom screen compliments the gameplay well, allowing for quick inventory management and relic switching without much trouble.
The analog circle pad slider doesn't feel ideal for 2D grid-based platforming, since you have to move it the furthest it can go in each direction to move your character, but if you're quick enough it'll work (or you could just use the D pad).
The action is also a bit small if you don't have an XL, so sometimes enemy projectiles can be indistinguishable from the background (although upping the brightness makes a big difference).

There aren't many more 3DS-specific adjustments that I noticed (I don't have/use 3D so I have no idea how it is), so I'll leave it at that.

If you're unsure if you should pick up this game, you should, especially if you like old-school 2D platformers of any kind.