ShroudIn part one there is no reason you can't clear if the casters are lazy/bad at it. Between BB/implosion/cometfall you should be able to quickly destroy the groups of mobs at a portal. If your DC's for implosion/destruction aren't good enough run ahead to the next portal and put up a symbol of death. If the casters are doing well then run one portal ahead and try to get a full stack of DP's on the portal. If you need to heal in this part
get a new group use bursts.
In part 2 your role varies depending on if your group decides to go NE divided or all S then split. If NE then pick a boss and DP them. (Orthon goes down really fast). Spot heal as needed (really shouldn't be much healing required). If all S then damage whatever until they're all down to about 10% or so. At that point try to get a DP on each on so when the group splits they go down easier (start with the slower moving).
In part 3 make sure you have death pact on. Be good at the puzzles (specially the 5x5's). Clerics are one of the only classes who can survive the wall (if you have DI). Of course if it makes it to the wall then
find a new group enjoy looking like the best cleric evah!
In part 4 make sure you have implosion. Use implosion to kill all the devils no matter how much people whine because they wanted to save one
When Harry comes out to play target the melee with the highest HP,
try to stand close to the other cleric solo heal, and start out just a couple paces back from the party on Harry. Once the first wave of the blades passes you should be able to step back through the gap to avoid being sliced as you heal. You should be able to keep the party up with mass heals. If you have to you can toss a mass crit to keep those with < 300 HP up if you're feeling nice. Personally I like to stack DP on Harry in-between my mass hjeals. If anyone died in this part and you have scrolls of raise dead you can raise 2 people without any trouble.
In part 5 buff your party then stack DP on the boss of your choice. Once the fight with Harry starts stand near the other healer and mass heal/dp with mass crits when needed.
(Is this the type of breakdown you're looking for?)