3dSen, an upcoming Emulator currently in development is now going through some Beta testing. Unlike some other Emulators, it doesn't just support old games, it aims to redefine them.
Allowing you to play the classics with an entirely new twist, in 3D with some depth to them and the results are pretty astonishing. The growing list of supported games is impressive, considering it needs a lot of tweaking to get them all right. It supports Linux too, and it's made with Unity so it works quite well already.
Here's a very quick look at Super Mario Bros. on Manjaro Linux with 3dSen:
It's going to offer Steam Input support, Save States, Dynamic Skyboxes, more game support over time and of course the entirely different way to experience the games.
Emulation is essential, I've said it before and I firmly believe that they are needed to prevent classic games being lost to history. With applications like this taking things a step further, it's quite exciting.