If M.U.L.E. sounds like it defies description, you are somewhat correct. M.U.L.E. does not fit neatly into one genre. There are 4 colony members. Since you need food and time and energy to produce goods, the auction is where a lot of the fun of the game comes in. For example, say your friend needs three units of food, and you're the only one with surplus.
Man is that fun.
You don't know how many times one of us would go home pissed at the other, only to call that night and set up a game for the next day. There are so many twists and little bits that add replayability to the game. Playing against your friends is so much more fun than going at it by yourself. Also, because the game's economy winds up changing from game to game, each time you play is a new experience. I am also leaving out the arcade element of the game completely.