Example prime might be the Ethereals. They were an amazing group. The Consortium was Goblins except with actual charisma, business savvy, common sense, and inventions that worked. The Protectorate was a pretty badass group of elite fighters battling the forces of darkness. Even the Ethereum had a story of tragedy and corruption to make the Scarlet Crusade look like amateurs at the whole fanatic game.
But in Wrath? Okay, we get some Ethereum hanging out with Malygos' posse, but that's it. Poof. Ethereals are all but gone. I would have loved to see them selling their Eco-dome tech to settlers in Northrend's snowy areas or something, or handing us monthly gem bags for Frost Wyrm Ivory.