As others have already said, MIDI is a spec and does not contain any actual sounds. General Midi's big thing was probably its defined list of sounds but that was really only a naming convention.

The great thing about MIDI is that it is easily routable to any number of things (physical instruments, samplers, etc.).

Being able to listen to Sonic 2 - Chemical Zone with a combination of a Minimoog Model D and a Jun-6 (basically a Juno-6) is unbelievably fun.