Thing is, Flash, Double Dash presented that mode as an option, not as a multiplayer mandate. You can race in multiplayer with every player having their own kart (2 characters then to each player). Nothing wrong with options, and that kind of "1-1/2 player action" deal can help open up the game for people who just aren't good at gaming. So I won't say it's a bad thing. You're right in that it's no substitute for a full multiplayer, but it wasn't presented as such.
I don't care about the other argument, but I'll just say this:
Snaking wouldn't be a [tornado fang]ing problem if the items were balanced. Bikes would also not be a [tornado fang]ing problem if the items were balanced. It wasn't a problem in MK64, and if it was, you just plain sucked. This is why every Mario Kart after MK64 has progressively gotten worse, because of how poorly the items are balanced. This is why no Mario Kart game will ever be as good as MK64, because they'll never go back to that item system again.
To be fair, snaking in pre-DS games, while possible, was MUCH harder to pull off and generally less effective. In DS any idiot can snake, and everyone and their dog knows the ideal character/kart combinations for it (BALANCE FAILURE).
But I'll agree on item balancing. I jump between 64, DD, and Wii a lot, and Wii has a unique way of generating extreme chaos while at the same time leaving you feeling relatively powerless. Banana peels are worthless, the 2nd place racer gets garbage, and near every new power-up in the game either hits groups or causes an item drop. My, how the mighty Triple Red Shell has fallen...
DoubleDash may not have item mechanics up to 64's level, but it was still decent, the game IMHO better than those MK's that followed (DS or Wii). Blue Shells were excusable due to the generally moronic AI, and those signature items which were NOT nerfed versions of 64's items (Triple Shells, or the COMPLETELY POINTLESS Golden Mushroom) actually worked quite well. It adds to the point of the 2-racers, mixing signature abilities and such. And yes, as PB said, you can hold any item in reserve with your driver. The idea was great, and I think had they taken the simple step of NOT having triple items juggled, and thus dropped on impact, it'd have worked even better.
The "disarm" mechanics are one of my biggest issues with recent kart games, really. If you're going to do it, do it with ONE all-powerful-with-some-practice-to-master item, like Starman, not half the damn arsenal.