I've never understood what people dislike about Double Dash, apart from the earlier level designs (the last Cup is incredible).
I liked Double Dash, but...
1) The physics seemed a bit floaty [tho not nearly as horrible as Super Circuit] 2) The graphics engine for the most part made things too shiny & plastic compared to 64 [this would plague all of the Gamecube Mario games besides Strikers; Mario Party 8 and Super Mario Galaxy have reversed the trend] 3) The *later* stage designs [Dinosaur Park among other desperately needed rails]
On the other hand, the many new characters were welcome, the stages were mostly good, and it was still a great game overall. However, MK64 & DS felt akin to each other in a good way, and the ones in between...didn't. Hopefully Mario Kart Wii will have followed in their footsteps.