The actual racing portion game is OK and isn't anything to write home about, as others mentioned. Then again, this was made in 1983, and there's only so much you can put into a game within the system/memory limitations. That's where the game's namesake comes into play, the pitstop. It's fun to fix up as much or as little of your car as you want -- the race against the clock another factor! (Blue Max and Star Raiders also used this to good effect as time to complete a mission also determined your final ranking.)
Another good idea was that your car gradually deteriorated (e.g., tires wearing out, gasoline running low), instead of exploding right from a collision. You also had to watch how you filled up the gasoline, as it didn't automatically stop once full. If you overfill, the tank empties and you have to start over.
One advantage over games like Pole Position is that you could actually bump into other cars without immediately bursting into a flaming ball of pixels. Pole Position was a much more realistic, believable, and colorful game, from the racing aspect though. Pitstop was a little too overhead, with not too great a control scheme, or maneuverability. The "Pitstop" part of the game was cool though, and added some depth.
I can't remember another racing game having user-controllable pitstops until the very recent F1 sims. The game itself was otherwise quite ordinary - the usual 'you've got the fastest car and just have to dodge very slow cars' thing.