I thought it's predecessor Mario Kart DS was the best game in the series except for the original. I was really excited for Mario Kart Wii, though while I did like it the only thing it added to the series was the ability to ride a motorcycle.
There was also online game-play which worked fairly well. I loved online in Mario Kart DS, but when the community learned a simple trick to boost their speed to insane levels, it ruined the fun. So having a new alternative was a nice option.
Though while it wasn't as fun as Mario Kart DS, Super Mario Kart, or Double Dash, I did really enjoy Mario Kart Wii. It wasn't the greatest in the series (nor the worst in my opinion) I still had plenty of good memories. Just don't use the Wii Remote with the steering wheel shell, much easier with a real controller.