In MMOs the Warden is typically a druid like class with close ties to nature. In Rift they specialize in HoTs similar to a WoW druid. In Dark Age of Camelot Wardens were a healing class with strong buffs with ties to nature that was also very tanky. Its pretty much in the same boat as the Bard. Both are great classes that are very fun to play and bring a lot to raids but they dont have a place in WoW.