While almost unchanged, it was known as Mario Circuit in Brawl and has been in the series ever since. It's based on the Mario Circuit Courses from the Mario Kart games, but it's not based heavily on one incarnation as the course has changed depending on the Mario Kart you're playing.
The biggest thing to look out for is the Shy Guy in the race karts. Sometimes you can stand still and make it out unharmed. They can attack from the bottom road or from the ramp overhead.
But they pack a decent punch if you manage to get struck. I didn't realize it until now, but it's possible to knock the karts back with an attack. But since they're so many of them, you're probably better just evading them.
While not my favorite stage in the series, it's one of my favorites. It's simple, it's got things to look out for, it work