Unlike MechWarrior 3, the Pirates Moon expansion gives you more to work on in terms of mission flexibility and goals, new mechs and some deadly new weapons like the Thunderbolt missle. You are able to do various objectives in a mission in order to complete the overall goals, in some scenarios you have to destroy a comm ray which would lead you to a different mission where you would be doing raids on other facilities like that and eventually wind up invading a base which would make it easier to finish that mission, whereas you could risk going in and invading your enemies base straight up.