WC3 at least tried something different, and their core mechanics spawned Dota and eventually an entirely new genre. WoW, as dated as it is now, was quite solid at launch and through its first two expansions as well. You'll note that Blizzard was acquired in the same year Wrath came out and how things gradually went downhill from then.

It's actually pretty important to pay attention to the staff members of games companies, as the critical creative and technical minds behind good games are likely to continue to make good games at different companies. When they leave a company though, it's a coinflip as to the quality of what that company releases later.