Alex the Allegator is really awesome, and so is supertux (and supertux 2 i as
far as I remember).
Though it is a controversal topic, i want to point out that for people
actually make mods and hacks of old snes/nes roms and share them with the
community, so they are exercising freedom 2 and 3. Freedom one is a
precondition for this anyway.
I guess none of those freedoms are really granted by law, but I don't know of
anybody who ever got in trouble with those old games. You can play them with
a free software emulator.
For me, they are acceptable from a freedom perspective but for other people
here they are not, so it's your decision.
However, I'm fully convinced that they are not the same thing as proprietary
software and that's the reason why i mention them here.
The Snes and Nes offers the greates game classics ever made. Personally, i
think that modern games can't compete.