I enjoyed the GH missions. Unfortunately it's not worth it time wise to repeat them. The further along the chain you get (you must complete one to access the next one, and be the appropriate level) the more complex the mechanics get.
:: Bosses that resummon one another
:: Failure if boss is killed before conditions are met
:: Multiple-spawn location dynamics
:: Enemy holding / Raid focus target / healing
:: Crowd control
:: Pathing enemies
:: Enemy Agro mechanics (I think there's a hate reset)

They're a very diverse set of objectives with huge rewards for first time completion.