Truth is, it's neither.
Weighed on its own merits, Starcraft is an extremely well-crafted game, albeit one with a few notable problems. The story is compelling enough to make playing through all three worthwhile, and the campaign difficulty is tiered so that each is more challenging than the last. You don't have to go through a set of training missions once you've already mastered one side. There is a good variety of multiplayer game types, and you can easily download new maps. Multiplayer has its own set of negatives, the major one being the predominance of rushing.