The best RTS you are going to find right now
But, of course, the biggest experience with this game is the online experience. It is incredibly fun to play multiplayer matches online, whether you want to team up with friends and do 2v2/3v3/4v4 or you want to just duke it out with random opponents one on one, the online league games are a lot of fun and very exhilarating. It's fun to have played for a year and a half now and to see the meta game change as time progresses. Blizzard does a great job of keeping the three races well balanced, and its great to see how players can constantly find new ways to use the same races and units to come up with completely new and bold strategies.
So, serious league games aside, starcraft still has a ton to offer online. You can play in a free for all game if you simply want to goof around and not focus too hard on the game, which is a four player match where it is every man for himself. Then, there is a plethora of custom games that users have created and uploaded that you can play on. These custom games can range from tower defense games to zombie survival to 1st person shooter rpg's etc. There's also standard 1v1 custom games that you can join, so that you can practice playing actual starcraft matches against random opponents, but not have it count for your leagues and ladders.
Overall just a superb game with so much to offer. Can't wait to see what is new with the next edition, Heart Of The Swarm