"Super Mario Kart 64" is a very fun game and much better than I expected it would be. When it came out in '96 I didn't buy it straight away, but a few friends of mine owned it and I got really good at the game -- and found it really fun to play.
Later I ended up buying it used at a game store and played it all the time. It's a really addictive racing game and elitists will be surprised that just because Mario is attached, it's not a cash in (like Mario Tennis and Party) -- it works well with or without Mario and, like "Paper Mario," doesn't sacrifice gameplay to target towards the little kiddies.
This is a great racing game AND a great Mario game. It's got fun features, well-designed tracks, fairly decent graphics for the time period (remember N64 was top of the line in '96) and a great two-player battle option.
All in all, a must-own if you've got an N64.