That's a pretty broad statement, isn't it?
I think video games are like any other product, in that most of them aren't going to stand the test of time -- but some will. Take movies, for instance. For every "timeless classic" that we still enjoy watching 50 years after it came out, there were a hundred or more that deserve to rot in some film vault.
It's the same with video games.
Pac-Man, Tetris, and Galaga will always be good games.
As for M.U.L.E., it always appealed to only a subset of gamers. It's about economics, it's about competition, and it's most fun when you're playing it face-to-face against three of your friends. For the gamer who only likes shooters (whether we're talking Doom or Space Invaders), M.U.L.E. will seem boring.
But for the people for whom it was made, it's still a good game. It is to me, anyway.