Oh man, I loved hacking on this game back in the day because the file structure was so straightforward and the code so transparent you could change basically everything, including textures, sounds, car types and interactions, physics - the whole lot.
Sadly, I haven't seen anything else since with that low of barrier that was as much fun to use. Motocross madness was another good example of that as well.
*Edit: I was actually thinking of Carmageddon 2 but its all about the same
MCM2 was my first introduction to this. The hacking of the game was just as the game as the riding was. These would be good examples last week when there was discussion about bugs in Minecraft being just as much Minecraft as the intentional features.
Sadly, I haven't seen anything else since with that low of barrier that was as much fun to use. Motocross madness was another good example of that as well.
*Edit: I was actually thinking of Carmageddon 2 but its all about the same