I wish I could finish it, but with my computer bugs I can't, and I thus don't feel that I can honestly rate. (The farthest I made it was to the first speed line jump). What I did see was great though. I do wish there could have been a bit more background (at least in the areas I saw), as while I agree with kiethy I think the beginning was a little plain (maybe could've changed the all-purple lines to have colored borders or something... idk, I'm not the designer lol). But as far as I could tell, I would have given this a 5/5.
Supermario, you have succeeded in making something so wonderfully fun and so perfect that it deserves nothing less than a slide and everyone's attention. This is the kind of level that I could play over and over again without getting bored. Not only that, but it is so perfect for racing and hopefully will hold many highscore fights. You've shown it's possible to make a level perfect without having to have tons of background.
Well done on your perfect level Supermario, and I really hope this gets you a slide :)