I just finished playing Blizzard's Warcraft 3 yesterday. It was a pretty good game, but I don't think I enjoyed it quite as much as Starcraft, although I'm having trouble putting my finger on exactly why.
Since I'm much more a fan of the single-player missions than of multiplayer combat in these games, I think it had to do with the missions. Warcraft 3 did have some things I really liked, such as the hero focus and ability to adventure at times as if in a RPG, but there were many units which you didn't get to use until the final mission, and I found it to be lacking that special something that Stacraft had. Perhaps it's that the races aren't as unique and different from each other as Starcraft's. Perhaps I missed the seaports and water units that Warcraft 2 had. Or perhaps I was just annoyed by the 3d engine. At any rate, I still prefer Starcraft.
Edit: I've figured at least part of it out. Even in the later missions, Starcraft allowed you to build your base from scratch, and research all the upgrades. Warcraft 3 always starts you out with a fully built town, and often gives you the upgrades.
I'll probably eventually play the expansion - Frozen Throne - but for the time being, I may go back to Arcanum or Temple of Elemental Evil.