Remember Micro Machines? Well Karnaaj Rally (who thought up that name?) is similar in that it has you looking down from above the action and you fire things at your opponents.
The main aim of the game is to wins races in an attempt to move up to faster leagues with batter cars. And it does start at the most basic possible level. The initial races see you in a Flinstones style caveman car. Once you have won some races though it makes quite a large leap (a few thousand years) to cars from yester-year, with another couple of steps to modern day sports cars.
The main thing you notice about this game is the graphics. They are extremely detailed and make this one of the best looking games on the GBA. Unfortunately, the sound isn't quite so spectacular, but is good enough. Gameplay is OK. If you liked Micro Machines you'll probably like this. The only problem is that it is just too easy. I finished it in no time at all and didn't feel any desire to go through it again.
So, to sum it up, it's a good game, but a very, very short lived good game.