Tyranyuz is right the online asspect of the game is real cool. If you have the basics of micro(clicking and moving). Go ahead on hook up to b-net. If are a familar with on-line gaming you will understand if some people call you a noob(some one that is not so good). I find b-net a very competive enviroment.
But I enjoyed the single-player asspect as well. You get to play all races. So this gives you a feel on what race you may want to play on b-net. Or you can also play random which is the best.