I bought MechWarrior Mercenaries before I bought this as I wanted to see what I was missing out. I'll tell you what I was missing out on. A lot.
Mechwarrior 4. AFter the patch from Black Knight Expansion was put in to correct a few minor flaws the game purred like a kitten. The starting cinematics are excellent and really give a feal for the game that is echoed all through the missions and briefings and further in game cinematics. The missions are mostly good, some are near impossible I found, but that's probably how I play the game. Some of the later mission are deadly and depending on how you choose the last two missions decides the closing cinematics. A very nice touch. The mechs can all be set out as they are required, necessary for some of the mission.
Black Knight Expansions: More missions and mechs and maps for the budding mechwarrior to hone his skills. I didn't find these as enjoyable as the first ones though.
Mech Commander 2: I don't like this game as I don't feel as in control. Taking command of the mechs from the aspect of the mission controller and maneauvering the mechs around the field instead of sitting in the cockpit is a different take on the game and one which I know some people really enjoy. For a better review of Mech commander 2 there is probably one somewhere else in Amazon.
Over all this is a good pack and I bought it for the Mechwarrior 4 parts and was pleased with what I bought.