With the Possibility of a new mechwarrior I had to come back and look at this game.
The mix of missions and the ability to increase your skills in the Arena make it eminently replayable even before the age of open ended campaingning. I just bought a uber system and am going to reinstall and see if it still plays!
I actually replay missions in my head to this day to help me fall asleep...maybe that is a bit much but true...lol