My son got this as a gift and he LOVES it. He never seems to tire of racing the cars round and round. He even likes to try push the cars up the ramps. In our experience it worked with almost all of our Hot Wheels and Matchbox cars. There were only a few that were either too long to make it around the curves or two wide to go down, but the majority worked just fine. Some cars go faster than others, which makes the racing more fun. The only annoying thing is that the track makes race car noises and says things like "Speed, I am speed" and "You're one gutsy race car". However, you can turn the sound off or just remove the batteries if the sounds make you nuts.
Edited to add: I wanted to add that it works with most Matchbox style cars, but most of the actual Disney cars from the movie Cars do not work. They are mostly too wide for the track.