I was disappointed in Warcraft 2 and Diablo 2 (although for different reasons), and World of Warcraft. I did enjoy Starcraft though (even if it had its own problems) and Diablo 1 was an outstanding game (which also had its own issues).
Warcraft 2 had too many limitations on how to control your characters, and jsut wasn't as fun as Command and Conquer. Diablo 2 was just a minor incremental update to Diablo 1, and I was already burnt out on Diablo so the second game didn't feel fresh at all to me. World of Warcraft had just a horrific UI, where it took me probably a half hour just to figure out the unintuitive control scheme, and it just wasn't fun once I did anyway.
I don't understand why Blizzard is held in such high regard. They make some very fun games, but they are far from perfect. They are better than many studios in that they have some very good quality control measures, but they have they failures as well (they generally fail to innovate, but instead rely on polishing established gameplay techniques.)