Well I finished Guardian of Tyria (and maxed title number 15 for IVI) last night. I actually thought the jungle missions were some of the hardest as me and one guildie cruised through the desert and the shiverpeaks with all hero teams. I think for the entire 25 mission sequence the most people that we needed was for Hell's Precipice which included six highly experienced players and two heroes. I would say that the most important thing in doing this is to know the missions, use the appropriate builds and be patient.