Still the best RTS to date....
StarCraft, with its expansion Brood War, is the premiere RTS game -- and still is, 7 years after it was released. It is the bar by which all other RTS games are measured.
Its short learning curve, fun gameplay, and strategic depth all add together to make an incredible game. The storyline is well thought out, and very well presented with in-game cutscenes and cinetmatics at the end of each campaign. The new units added to each of StarCraft's three races are each useful, blanaced, and fit the 'feel' of the original game. When I go back and play original StarCraft (without Brood War), I feel as if a part of the game is missing -- that is how well Brood War fits melds into the SC universe. Any RTS fan that hasn't play this game should pick it up immediatly. I think you can find it for $10-$20 (that is, both SC and SC:BW together) these days. I assure you, you will be playing it for a long time to come.
I'm still playing it.