Wow. I want to throw my 2 cents in on this Mario Kart madness.
I agree DD is the worst MK game. The main reason why is it is the most luck based game in the series. At the time it was out I had a roommate who was a master MK64 player. Previous to DD release, we would still have lots of friends over and have MK64 parties. In Vs. racing, he won 2/3 of the matches, with 4 players. Skill could trump random items.
In DD... everyone won all the time. Learning tracks, selecting specific character items... none of is could overcome the random AI and ridiculous amount of blue shells. Not to mention the Cup races against AI. I can't count the number of times I got hit by blue shells in
2nd place by the ridiculous AI. Unlocking 150cc and mirror modes was one of the most painful GC experiences I had... 2nd only to F-Zero GX story mode.

DD is a luck-based crap fest. Thank goodness we can still hook up MK64 when people come over to play. Or even MKWii, which still isn't as pure as MK64, but online play with 12 people is its own bonus that makes the game fun in a different way.