It really depends on the whole party, though more heavily on tank and healer. ...wipes on the early monsters usually come from tanks pulling more than they can handle, unless the healer can make up for it.
The poison debuff / fruit parts can also put extra strain on the healer if the dps wait too long to eat fruit, or don't eat it at all. But otherwise it's not a problem with regen or a bit of aoe heal.
2nd boss, doesn't matter too much if the dps don't know the fight (for ranged dps, anyways) - if the healer and tank do. The dmg on dps isn't hard to heal, as long as you don't get hit yourself as healer (paralyze).
And well.. if the tank and melee dps don't move out of the 100-tonze swing, it's a one-shot on the dps and a big piece of the tank's hp (...or one-shot if undergeared).
And last boss kinda same as first boss, just with the exra bit of killing adds with aoe. Healers can help out on that with cleric's -> holy, or clerics -> dots + bane (and maybe a little Blizzard II spam).

(...what's up with the 1000 characters post limit? That seems.. way too limiting. Had to crop about half my post xD)