The 3DS, the successor to the Nintendo DS, improved upon the initial design and even with its rocky start, it proved to be a very successful portable gaming device.
Despite the name, the 3D features is not the reason it's on this list. That reason would be the Street Pass.
Street passing is a mode included in several games on the 3DS where the player walks around in public with their device on standby mode (with the case closed) and passes other people doing the same thing. Data is shared between these players for the next time they open their 3DS. What happens with that data is dependent on the games they had.
Street passing is a feature in many games that's often optional, but adds a layer to the game. But the real genius of this is how it gets people talking. The 3DS sparked so much conversation when seen peaking out of someone's back pocket, while the actual addition to gameplay was minimal. It's as if Nintendo wanted to find a way to get people to talk about their product and built a function specifically for that reason, and it worked!