I'm inclined to agree with goonernumber1 - easily one of the best games I've ever played. Packed with humour and character, loads of great missions, great story and plenty of sweating! Dated looking now but I remember how incredibly good it looked after its predecessors, and how damn exciting it was when I first got my hands on it. This is a true, all-time classic, a real milestone in the history of gaming.
By the way, the origins of the entire build-a-base genre stem from the great-grandaddy of them all, Dune II, which was followed by a couple of Command & Conquer episodes and then Red Alert.