Since you're talking about monster stats/player balance and I see a lot of threads about EE versions of this pack, I'd like to add my thoughts on HE to show a comparison and help bridge the gap between the massive difference of an EE and HE scaling.
Disciples of Shar: (Ran solo, no hire, Monk16/rogue1) This quest is very well balanced, the mob density, saves and health is in the right place, with the exception of the orange lionesses, They have way too much hp. I don't know if this quest scales like The Druid's Deep chain, or like the Rest of Wheloon, but it's nice to not have to wade through sacks of hp (even if the quest is very repetitive).
Escape Plan: (Ran with a lvl 17 fvs hire) 72 Lizardfolk in the first encounter (larger than a platoon)... That wouldn't be horrible if they weren't mostly sacks of hp, and about 2/3 of them are. The Warriors and Archers have too much hp to be in that encounter, the scavengers are about right. The end fight isn't bad, except the constant spawn of mobs, this is bad mechanics, as the only way to deal with it is to kill all of the spawns except for 2-3 and then kill the boss so that he doesn't keep spawning trash.
Shadow of a Doubt: (Ran solo, no hire, Monk16/rogue1) This quest feels like it has the same scaling mechanics as Druids Deep (more players means more enemies, more hp, and more damage), the biggest flaw with the quest is the instantaneous swarm of 16 shadows right off the start. With no option to break the group apart and fight them in smaller numbers, and their ability to stack on top of each other so you can't use the corners to reduce the number that can hit you, they are easily the hardest part of the quest until the boss. The rest of the quest feels good if you use the npcs around the quest to act as your meat shield to reduce the numbers directly attacking you, and I like the end boss... except after a certain point he spawns an endless wave of shadows that have too many hit points to be an endless wave of attackers.
Friends in Low Places: (M17,Ro1 and lvl 17 fvs hireling), I like this quest, it's a little repetitive, but not terrible, just curious as to why the hp of the mobs scales so quickly (17 gave 600-800, 20 has 1100-1500, and 21 has 2200-2500). The end fight is poor design though. The boss is good, but there is no reason to spawn 20-24, 2500hp guards all with stunning blow right off the top, as well as two additional waves of 10-12 throughout the fight. The dungeon alert gives the red name broken punitive defenses and buffs (designed for preventing zerging, not for added challenge to boss fights) and though the spawns hit for a decent amount of damage, they have too much hp and all have stunning bow to spam against you. I'd hate to see how these numbers scale if that's what they are spawning for 1 player with a hire.
A Lesson in Deception: (M17,Ro1 w/ lvl 17 fvs hireling, and 16 Monk w/ lvl16 Cleric hire), This is a good quest, on HE I didn't see anything wrong with it, the scaling worked great (the mob hp/dmg wasn't doubled [perhaps do to the level composition]) and there were options and choices to be made throughout the quest. This is easily the best in the pack.
The Thrill of the Hunt: (M17,Ro1 w/ lvl 17 fvs hireling, and 16 Monk w/ lvl16 Cleric hire), This quest has potential, the only problem with it are a game crippling flaw, and a poor spawn count of potentially interesting mobs. I like the boss, it's too bad that bad mechanics make this fight a 'range or die'/'find an exploit to counter our exploit', our party caused the highest Orange Alert, just on the verge of Red. The issues with the assassins and howlers will be summarized separately at the bottom.
Army of Shadow: (M17,Ro1 and lvl 17 fvs hireling) It's a good quest, with the exception of the high hp shadows with annoying mechanics and large spawn numbers, with the large number of assassins right before the end fight. On HE the bosses are good, fairly well balanced, the wurm does attack slow enough that he could possibly get a damage buff.
Through a Mirror Darkly: (M17,Ro1 w/ lvl 17 fvs hireling, and 17 Monk w/ lvl17 Cleric hire), I want to like this quest, there are a lot of optionals that can be taken, the mechanics of the quest are interesting, and it's not too complicated. I can't like this quest because there are too many assassins in each instance. The end fight is either trivial or poorly designed, depending on the side you fight on. On the material plane the mobs are the right strength/hp, but need to be more dense. On the Shadow Plane, they have too much hp and cheesy mechanics.
Which leads to two side points for the entire Wheloon chain, Shader-Kai Assassins and Howlers. I like both creatures' designs (With the exception of Howler Quills), but they come with one shared problem, you cannot spawn that many of them at one time!
Shader-Kai have an interesting skill set that shapes and evolves the combat dynamics, it forces melees to not just sit there and take it. But you cannot spawn 4-6 of them in a single encounter, because then the interesting mechanics become cheap, annoying, and go from being interesting to being poor mechanics (I don't know if non abundant step toons can deal with numbers in that size). Limit the spawn count to 1-2 per group (give them a pull attack if you must to bring ranged characters to them), and don't scale this up with party size (they have an aoe attack, you don't need to add more). On HE, the Saves, HP, and Damage are fine, it's only their density that is affecting game play (I'd like to see more mechanics like this used sparingly to target different aspects of game play).
Howlers, they too are interesting, I like what they can do, and fighting Orange and Red Named Versions of them aren't bad (less interesting as they devolve into the hp bag that does damage). But the common versions spawn in groups of up to 16, they have a lot of HP, too much for their density (2,500?) have stacking debuffs that see no limits (in saves, stack size, ability to use them and annoyance). The Quills have a 60 second duration, stack indefinitely? (I've had up to 17) and the DC to save against them is larger than 57 on HE. Drop the duration to 10-12 seconds, limit the stacks to 10(it might be interesting to change the size of the stack based on difficulty), and lower the saves to 46. The Howl stacks indefinitely (who needs a -64 wisdom debuff?) and doesn't need line of sight to apply. Actually stack this ability (I don't need to see the icon flood my screen) and limit it to 10 stacks (-20 wis). I'm fine with the density being as large as it is (so long as they don't count towards Dungeon Alert), give them the a high to hit chance and the ability to hit through concealment, lower their hp to 600-800 range, make it so the pack can't be divided, and lower their damage so they apply constant low damage pressure.