Solo play also has a much greater range for changing the game. Where MP seeks balance so that the winner can be decided by their strategy and tactics, solo play thrills to extremes. Both the high and low ranges can explored. I suppose an example of that would be that the chaos games on my server still get regular play.
Edit: for those who havent tried them the chaos games tries to give every province completely randomly selected extra units with random equipment. You starting army might include a Horror commander leading dragons, but then the independent province next to you might include a monolith guarded by angels. There are also extra castles, 3 AIs that are allied with each other, and 2 special AIs representing the independents (BIG surprise to have the independents attack your province from next door with a mixture of independents units). NOT recommended for new players. Its an extreme and sometimes unplayably rough game for the jaded oldtimers.
http://www.Dom3Minions.com