I have not read the article, but from the posts in here I get the impression that what the article calls transparency I would call metagaming.
Also the words "less transparent" have quite a negative tone to it (as transparent is generally considered a good thing), so its not a surprise that people get the impression that not telling player such informations is bad (less transparent).
The article is very clear that each group needs to find the balance that works best for it, so I'd say that any negativity isn't quite there.
Ok, for those of you who have not read the article but feel obliged to comment on the wrongness of it, let me give a general overview of what the article
actually considers 'badwrongfun':
The opening of the article is an excerpt from a hypothetical gaming session in which the players have been wiped out, and the DM shrugs off their complaints of difficulty by pointing out how poorly they've played - the mage sent his fire attacks against the fire resistant enemy, they kept doing small amounts of damage to a regenerating foe, and they kept fighting inside a mummy's aura of despair.
Except the DM didn't tell them that one enemy was fire resistant, that one enemy was regenerating, and didn't even let them know about the aura - just calculated on his own the penalties it was giving them.
I think we can
all agree that this sort of knowledge is information player's should have. Not necessarily known at the start of the fight (though the right knowledge checks might solve this), but the effects of this should be obviously revealed in gameplay. When you hit a fire resistant enemy with fire damage, it should be clear the attack did not deal full damage. When an enemy regenerates damage, it should be clear it is healing. When the PCs are under the effect of an Aura of Despair that gives them direct mechanical penalties, they should be aware of this.
The article then goes on to discuss various ways to solve this. You can do it entirely in character:
"The warrior laughs as you hurl your Scorching Burst, and you can see runes over his armor come to life and protect him from the attack!"
Or you can go the fully transparent route:
"Yeah, that guy has Fire Resistance 5. He takes 5 less damage from your Scorching Burst."
Either of these is an acceptable solution. What is
not acceptable is withholding information from the players that their characters should have. That isn't avoiding metagaming - that is ignoring the conventions of the game itself.
Are there enemies whose effects might be inherently hidden? Sure. I certainly favor reskinning enemies so they will be a mystery to PCs walking into the fight. But once the fight starts, hiding obvious capabilities should be an extremely rare choice, usable only when both the challenge and the flavor of the fight calls for it.
Once again - every group will have different opinions on what works best for them. How transparent they want things to be, how they want the DM to convey knowledge, what areas of knowledge should be conveyed. The article doesn't just welcome that, but takes an approach designed to help with whatever method a group is looking for.