I have very fond memories of this game. It was my very first Mario Kart game, and I loved it. But let's see if this game can still compete with the other Mario Karts in the series. Here is my review of Mario Kart: Super Circuit.
Graphics: 8
The graphics look pretty well for its time and for a Game Boy Advance game. Compared to other Mario Kart games, it's not the best, but it's still a pretty good game in terms of graphics. Compared to other Game Boy Advance games, it's definitely one of the best. 
Sound: 10
The music is some of the best in the series. The character sounds are well done, too. Some of my favorites are definitely Sky Garden, Cheese Land and Sunset Wilds.
Addictiveness: 10
I don't even know what to say for this part other than the fact that it's very addicting and that I'll come back to play it.
Depth: 9 
There's the usual Grand Prix and Time Trial modes with 3 engine classes: 50cc, 100cc and 150cc. But instead of only 4 cups, there are 5. There's also the SNES tracks in the extra 5 cups, which makes for a total of 10 cups. A new mode, called Quick Run, is also in the game. 
Difficulty: 8
Controls can be wonky at times, and trying to triple-star rank all the cups in every engine class can be a rough and rage-filled journey.
Overall Rating: 9
Mario Kart Super Circuit is a fun and great game, and also quite underrated. Trying to beat all the cups with a triple-star rank in every engine class could take years to do. The controls can be wonky on some occasions, but that doesn't reduce the fun factor. Overall, it's a great game and I highly recommend it for racing fans or just fans of Mario Kart, like me. 

You master the basics of game reviewing by clearly dividing your article into paragraphs (consider spacing them out a little, though). However, consider adding much more details. You say the graphics are good for Game Boy Advance; how do they compare to other Game Boy games? To other Mario Kart games?

The music is the best of the series; what tracks did you prefer?

janus :  This is my first review of any game, so of course I really didn't know what to say. I'll try to edit it, though. Thanks for the advice.

ShadowBlaze73 : No problem. We all go through that stage. My first review was less than 500 words. But now, thanks to feedback, they are at least 1500 words