Just a really nice game. It's fairly basic, all things considered, but there's a ton of developer-made tracks to drive through and a pretty powerful track creation tool that has naturally lead to an absolute goldmine of user-generated content to play.

You get loads of content here, and in a game that's completely free to download on Steam. If you like racing games, you should really play TrackMania Nations Forever at some point. It costs nothing and will probably run on anything with a motherboard.