MK: DD is definitely the worst Mario kart to date. They should have just upgraded MK64, but they took away something that just changed the game for me. The hop to power slide being one of those things. The rest I can't quite put a finger on, but that game was just missing something that made MK64 & MKDS so special.
Double Dash's partner system allowed for quite a bit of strategy when using and/or planning to use weapons. That, as well as the character-specific weapons, are something that is greatly missed in other installments.
This is what make DD for me. I had a friend who was my permanent DD partner. I was the driver and he was the gunner. We were awesome. You had to work together to pull off the mini turbos, you could swap items on the fly when needed, the gunner had better aim and control since they didn't have to worry about driving, and a good gunner could use the side lunge to steal items, upset opponents and to save your cart from an object with a quick side dodge. Though he sometimes went crazy with the dodging when we were in a tight pack and we would sometimes careen off a nearby ledge, but it was a blast. I loved how Gamecube games like DD, Crystal Chronicles and Four Swords emphasized teamwork and communication.
As for other GC titles to try, I recommend these:
>Metal Gear Solid: The Twin Snakes
>I Ninja, reportedly fun but I've yet to play it.
>The Prince of Persia Sands of Time, Warrior Within and Two Thrones
>If you like Suda 51's work then you could try Killer 7
>The Hobbit was surprisingly a very good platformer with zelda-like combat. Really well done.
>Custom Robo: Battle Revolution
>Skies of Arcadia Legends
>Lord of the Rings: Two Towers + Return of the King
>>>>Pac-Man Vs.!!!!<<<<