Fascinating.

I use the same controls as Buster:
Ctrl = Fire
Shift = Jump
Arrow Keys = Movement
Space Bar = Change Weapons

Perhaps not the best set of controls, but they suit me. I used them in another sidescroller called Hunter's Hunted (by Sierra) before I played JJ2, so I was accustomed to them.

The only difficulty lies in changing weapons...my pinky can press the space key fast enough, but it's a bit difficult to press the number keys while still running - so I just don't bother with the weapon keys. Perhaps those who use the default controls have the right idea.