I have it, and play it fairly often.  If you like RTS games and you'd like to try it out, hit me up on TS3 whenever you see me on, I have one guest pass left (which will give you two weeks to play the first installment -- Wings of Liberty -- and see if you like the game).  There is one expansion out already (Heart of the Swarm) but you need to buy the original game first for HotS to work.  You can also play some HotS matchmaking games even if you only have Wings of Liberty (WoL) as long as you are in a party with someone that has HotS, but if you do this you will only be able to choose the terran race.  Any person with HotS can roll-back to WoL when in a party with someone who only has WoL, and both players can do matchmaking games and choose any race.  The difference here is that the new units and research abilities from HotS will not be available when playing WoL together.

There's a steep learning curve, but after about 10 matchmaking games you should be in a position where you stand a chance against other players, especially if you have a friend explaining build orders and unit composition to you (that would be me ).

~Phoenix