The problem I ran into with Commodore was that many, many games used all kinds of different keystrokes. Like F3 to select difficulty, "m" to select mode, etc, etc. Take M.U.L.E. for instance. You're looking at 3 keyboard keys to start a 1P game and 7 keys for a 4P game. Unfortunately, there's no universality of keys to the game functions...
I sort of got it to work with automaps in joy2key and Rocketlauncher, but I still need to iron it out. It's hard to keep track of the button assignments, so, LEDblinky for that...