If you haven't played Warcraft II, pick this game up as soon as is humanly possible!
The fact that you can get both, Warcraft II: Tides of Darkness, and its expansion Warcraft II: Beyond the Dark Portal, along with access to Battle.net; Blizzard's way of letting you play the game online with people around the world; in one package is amazing. This is one of those games that is one you will find yourself replaying just for the hell of it.
The campaigns, four in total, one for the Human Alliance, and one for the barbaric Orc Horde, in each game, are done phenomenally. While it's missing some of the flash of newer RTS's, all the essentials are still there, and they come together just so to create hours upon hours of innovative gameplay that will keep you coming back for just one more mission long after you should've put it down.
Online play is, for the most part, great. Blizzard keeps servers up and running and has thus far managed to avoid hackers and any glitching that could possibly ruin gameplay. Whether your cup of tea is killing other players in traditional matches or playing special edited maps that feature a wide variety of play styles, Battle.net has it for you.
While many features, namely the online play, have been set aside by the majority of the game's fan base for the newer and shinier Warcraft III and Starcraft, the old school style and thought required to beat back the orc hordes or to Slaughter the puny humans, and demolish their way of life, is always invigorating and refreshing.