To get the best idea of what its like, try playing the first Starcraft. Your computer should be able to run because its about 10 years old. Its kinda hard to explain how good the game is since i don't really play RTS's that much so i can't compare it to other games. All i can say is that the 3 races you can choose from are well balanced, and very asymmetric from each other. The story mode is also a lot better from the first one. Its also very fun,and thats saying quite a bit from me. I usually get bored of RTS's in 20 minutes.
My Battle.net name is Jason (didn't feel very creative at the time) and number is 715.