First Blizzard game I ever played was Warcraft 2, and I really loved that game. Still do, I recently played the expansion, Beyond the Dark Portal, again. It was awesome!
After that I played Starcraft, which was a whole different beast. One of my favorite strategy games ever, and favorite Blizzard game, no doubt. Still have it installed on my PC. Later I played Diablo, WC3 and of course The Lost Vikings somewhere along the way, which is also a fun game.
They really used to make cool games. I play SC2 too, but something is just missing. Even with all it's flaws, the first one is still superior in my eyes. Haven't tried Diablo 3, yet.