Definitely one of the most satisfying RTS in recent history. Blizzard ups the ante from Starcraft to be a great 3D RTS.
Not only does the game expand and improve upon the great history behind Warcraft, its introduction into new areas and incorporation of new races makes this game a great achievement. Each of the races are pretty well balanced, but not direct unit duplicates of each other, allowing for well varied strategies and tactics.
The included map editor (*World Editor) is a behemoth of an application, allowing for mappers to create very complexed and detailed maps for custom games. This has spawned maps varying from Altered Melees, RPGs, Tower Defense, to 3rd Person Shooters. Making literally a limitless supply of well varied custom maps to keep the gamers coming back year after year.