Methedras asks once again over on WoW LJ if now is a good time to be playing the old Warcraft RTS games, and, actually no, now is probably not a good time to be playing them. You should probably be heading up to the Isle of Quel'danas and helping your realm and the Shattered Sun get those dailies unlocked.
But yes, after patch 2.4 has quenched your interest in the World of Warcraft for a while, now would be a perfect time to play Warcraft III and its expansion, the Frozen Throne. Because we are right smack dab in the thick of the lore following both of those games -- Illidan and Kael'thas' stories have just finished, and the main event, with Arthas Menethil, is just about to start in Northrend. Up until the end of Wrath of the Lich King (and we're just now reaching the end of the Burning Crusade), World of Warcraft was really just a gigantic, cross-genre, extremely involved and detailed sequel to Blizzard's earlier Warcraft games.
There are other places to go beyond this, however, of course, and we've discussed a lot of them before (and will again, no doubt). But yes, if you haven't played the RTS games yet, you've already missed half of the story. Now would be a great time to play them, before you miss the second (and in my estimation, much more interesting) half.