There is only one car. The only game mode is time trials. There is only one arena. From this simplicity arises genius: The one arena is infinitely reconfigurable using an in-game track editor, and the game is focused on online multiplayer action. Picture you and twenty other people racing against the clock, and the only thing that separates you from the rest is your skill. That is racing at its best.
The game plays a lot like a F-1 racer meets F-Zero. The car is small and fast. (Speeds typically range from 100-500, but the game lists no units) There are no gears to shift, that's done automatically. The car handles like a mid-engined formula car without any snap oversteer — the car is planted, you just have to tell it where to go. As you can imagine, the margins of victory are razor thin.
The graphics are smooth and beautiful. The scenery is always the same, but it always looks realistic with features like motion blur and bump mapping. If you found TN on a Xbox 360, you wouldn't be disappointed. I personally don't care that much about the visuals, but I know some people do.
The track editor is the spiritual descendant of games like Stunt Driver. The track pieces go together like slot car track, with curves of varying constant radius, banked track, and elevation changes. Tracks come in both flavors, the kind where you just have to get from point A to point B, and circuits. Jumps, loops, and obstacles add even more challenge.
Online play is smooth and enjoyable. Since TN only does time trials, there are no car-car collisions. You can drive right through the other competitors. A round lasts only a few minutes, you have to get the best time in that short window to win the round. Players from around the world play TN, and griefing is virtually nonexistent.
Adding all these things up, you get an arcade racer of the purest quality. Oh, and all this is free. You can download it from their website, no strings attached. (Sorry, windows folks only) The game is partly an advertisement for their other games, Trackmania and Trackmania Sunrise, but it also hosts a number of online championships.
Well, I'm out of potato salad... I'll see you on the track. :)