Ripzerai said:
It's not so much that the ogre mage's abilities were random - they suited a purpose. The purpose, essentially, was to make them vampires in the Bram Stoker sense.
Charm wasn't necessarily for using in attacking PCs (though that was a valid tactic in the days before CR). The ogre mage turns into mist and seeps into the bedchamber of an influential noble, charms him or her strategically, and uses sleep to bypass the guards if necessary. In this way the ogre mage slithers into the hearts of the area's power centers to bring power to itself, smoothing the way for its introduction in humanoid form. Everyone feels friendly toward the handsome new noble, even if they don't remember why.
I think this states it nicely and also applies to one my objections as to the rational that the rust monster needed a redesign. First let me say I like very much how Mike set forth his goals and then went about making the monsters better fit those goals. A nice example of design process. I also don't mind his design goals or philosophy, they are after all to each his own.
What I object to in the rust monster and ogre magi is the assumpation that the only way you interact with these creatures is by combat/fighting them and all abilities are judged in this light. Ripzerai gave a very nice description IMO of why the ogre magi can be more dangerous than a simple combat oriented view would suggest.
On the flip side, the rust monster is not so fearsome if you realize there are otherways to deal with them besides fighting, such as throwing them food. In the case of a rust monster you have non-perisable food in abundance, metal. I realize it is a bit of a DM judgement call, but what if the rust monsters loves the more precious metals (I guess their version of candy or steak). One tactic then is don't fight the thing up front, throw it some gold to eat and get out of the way. A simple "redesign" that placed this behavioral trait in a description on how to run them can quickly remove the "ruin your whole day" fear, at least for those who don't kill first and ask questions later. Maybe I'm alone in thinking there should be some monsters that are better overcome with brains rather than brawn.
I do like what Mike did with the slower armor reduction, which makes a lot of sense to me when going from the 2 min 1e AD&D round to the 6 second 3.x round. In actuallity, the armor might disappear faster in 3.x, as I always took the word "instantaneous" in the 1e description to mean within the combat round, which for game purposes is "instant", i.e., happening before you can do anything about it.
In the end what gets me is not the end designs, but the implicit assumption that the only use of a monster that matters from a design standpoint is how it works in toe-to-toe battle and assuming that this is the only way a party will ever deal with a monster (or how the monster will deal with them).