Challenging to both reflexes and mind, good-looking, but most of all just plain FUN!
The game looks good. REALLY good. I think the engine has been upgraded a little from Sunrise. The textures look good on everything, the shadows are pretty much dead-on, and the reflections (especially on the surface of your car) are downright impressive. But that's just on the surface.
The game itself is as fun as always. I always describe the games in this series as "driveable hotwheels tracks" and I stand by that. The physics engine, while fairly realistic, takes quite a few liberties in the name of sheer fun (such as being able to accel or decel in midair). That's a good thing. I haven't ventured online yet, mainly because the solo mode tracks (all NINETY of them) are keeping me plenty busy. The difficulty seems to have been ramped up, which is both good and bad. On the one hand, I'm never bored. On the other hand, a few tracks have been very frustrating for me. Fortunately, there are about 87 others to keep me happy.
They improved a couple things significantly from Trackmania Sunrise. One is the music. Yes, it's still fairly repetitive Europop-ish stuff, but there's more variety now and it's of a slightly higher quality. Also, the switch to F1-esque cars, while almost entirely superficial (they handle just about the same as Sunrise's slick sportscars), is kind of an interesting choice, and the stadium setting lends a good sporty feel to a game that was designed to be and international competition.
The one bad thing: Replays. Given that this is the third game of the type, you'd think they would have found a way to let you change the camera angle in a replay, or even PLAY THE BLASTED THINGS BACK after you've saved them. I'm sure there's a way, I just haven't found it yet, which is a pity because I've saved some pretty impressive-looking feats already and I want to stroke my massive ego.
In the end, there's a very simple reason everyone should play this game: It's FREE. Utterly, completely, gloriously free. Even if you don't like the game that much or find it frustratingly hard, it only costs you the download time (it is a good-sized download) and install space. Furthermore, you can bring honor to your country with you l33t r4c1ng sk1llz, and, really, who hasn't wanted to do that at one time or another?