Although the single player aspect is good, this game is a real gem when multiplayer component kicks in.
Aside from being able to choose from conventional head-to-head scenarios, you are able to play through the campaign in coop mode.
And thats not all: you have two avenues of approach - you can either play it as a regular RTS, or you can take direct control of a unit and smash the puny opposition :)
This will probably be the best spent 10$ in your life (unless you bought Apple shares a few decades ago)