I don't have (not yet ... <img src="/images/graemlins/grin.gif" alt="" />) a HH, but from my reading, I would say :
- a much much better (and flatter) sleeping surface, where you can sleep on your back, or side, and turn etc.. without falling out
- a smooth surface (no netting on which to get caught when moving in the hammock) ;
- a greater stability, when entering or exiting the hammock, with the special mode of entry/exit the HH provide ;
- a bug proof netting, totally attached to the hammock, without any hole ;
- a set-up time of about 3 minutes, hammock and canopy alltogether.

well .... I guess HH owners could give some other differences...