Just picked two of these up on the cheap today and will never go back. I think I am in love.
Features:
An identical D-pad to the standard 004 controllers
Separate turbo functionalities for both the A and B buttons
A and B buttons are identical to the 004 if not even more responsive.
The controllers corners are rounded
It is bigger, which is good because we are all bigger than we were in 1989
It has a headphone jack
It has a volume switch for the headphones
It has a switch that enables a sort of faux stereo sound