I ran this tonight with a group of 4 people all with level 1 characters.
The party was a ranger, oracle, sorcerer and a rogue. This wasn't close.
They wiped on the plague zombies (they couldn't hit and the zombies had a high initiative, pinning the group in). TPK.
Personally, I think that this should be a 3-7 scenario or make the 1-2 tier easier. The last fight is an absolute killer.
If any group that runs doesn't have a cleric or a person that can channel positive energy, it's a wipe.