While no single tech in SC is groundbreaking in and of itself, very few games, if any, are putting them all together in a single game. That, coupled with the scale and level of fidelity, is the ambitious part. If that isn't ambitious, then please, show me a game that was or is ambitious, show me a game that has already done everything that SC is doing.
That's really the big question, whether or not the game is fun and engaging once all of the various mechanics get put into place. Trading and Combat have been done to death, so I don't think we can use those to determine how the rest of the game will turn out; though if they can't get trade and combat down then we have something to worry about. I don't think we'll get a good understanding on how things will pan out until all of the Mining mechanics are added to the game. That'll be the first real job or profession where CIG will be able to give the players a good understanding of how everything else is going to pan out, what mechanics they add to the game to keep mining interesting, engaging, and fun.