So far we've all been quibbling over the size of the block, but I think we're missing something that is the biggest difference to me.
With the 3e Balor, I not only need the monster's statblock. Before the fight I have to look up all those SLAs, and review the Balor's Feats, and see how all of these interact with the rest of the Balor's stat block. Then I have to use all of this to decide its tactics. Then I need copies of all of these spells at the table for reference when the balor uses them.
With the 4e Balor, not only is the statblock smaller, but all pertinent rules are in the block itself. I do not have to memorize what a spell does, or have a reference on hand, or shuffle through a stack of papers. It's in one place, the same place with its AC.
I think the 4e stat block is a thing of (relative) beauty. There is little more than I would ask of a stat block than to allow me to run the monster/NPC in combat with all the relevant rules in a single location. 4e tends to require more enemies and more complicated GM tactics because - just as a general matter - the combat part of 4e is a much more complicated and tactically rich game than previous editions of D&D.
The problem is that 4e provides less help setting up the world and the internal logic of NPC-to-NPC interaction. The monster manuals are
much better than the WotC modules in this regard, but they are still thin on questions regarding how monsters behave and are organized. And they are also thin on non-skill/non-combat abilities like what rituals they are likely to know (whether or not these rituals are also accessible to PCs). To take a demon example mentioned above, it would be useful if there were sets of rituals commonly known to certain types of demons and devils (e.g. turning someone insane, long term mind control, etc...).
This material isn't completely absent. We know, for example, that mind flayers collect thralls, that hobgoblins tend to have monstrous "pets", that kobolds love traps and that otyughs like to hang out in giant piles of... well... let's say in gross places. But there needs to be more. As much as I found the three-ring binder format of the old 2e Monstrous Compedium annoyingly fragile, the combination of small stat blocks and large sheets allowed the writers to provide fairly substantial descriptions for many monters.
I like that WotC, as rules designers, have focused on rules that are relevant to PC interactions with the world. But too much of the "how do the monsters fit into the world" material is relegated to the Open Grave / Draconomicon / Planar books. And, even in those books, little space is given to non-combat special abilities.
Modules are a special case of this. General information on how creatures fit into the world is correctly left in the monster manual. However, there needs to be information concerning how the monsters fit into that particular scenario. I don't need to know if the 4th hobgoblin on the left knows how to cook, but I do need to know why the hobgoblins are there and what their leader is trying to do.
It's an interesting question whether the 4e philosophy of focusing on the combat stats has lead the same group to write bad modules like KotS. My guess it that the HPE1-3 modules were designed for "lowest common denominator" games, and that the module authors simply put more of their efforts into the core D&D products than the modules themselves. I recall a post by Mike Mearls saying that he didn't think KotS was a good module either. IMHO, it was a really stupid idea to provide a crappy module as the first introduction to 4e, but (as others have noted) it's the module - not the system.
-KS
