The main problems with DD were that there were no real shortcuts on many of the tracks (nothing like the beach jump or Star tunnel from MK64) and you couldn't really head 'off-track' much at all.
The jump was missing which made it feel a bit crap and if you managed to fuck your opponents up on a big jump, for instance, they got put back on instead of havin to go round again etc, this made it all a bit too 'nice'.
I think DD is just too 'kiddie' really.
MK DS is far superior.