I really enjoyed the 5 mans at the start of Cata, looking back...I thought they did decently well.
Looking back even further, Dungeons like Strat, BRD and Scholomance I really loved. They had there own personalities, lots of cool quests and very farmable for a long time.
I am at a loss of why they (Blizz) have the current model of gather everything up and nuke in a pile. Does anyone seriously like the current model? Forget about Raids for a moment, what would you like to see in 5 mans? Either brought back, an added feature, difficulty levels, gear for starting normal raids, rep grinding etc?