The second one focuses on unit dynamics, and you really don't do much base building at all. In single player I think the only building you do is plopping down sentry turrets as a special ability. It was very fun for a while, but the missions are extremely repetitive so it gets old. There's basically 2 types of missions, plus a few plot-point missions that are larger versions of the previous ones. Great idea, but they needed more variety.