I'm mulling over a house rule for DF Felltower.
I've long suffered ambivalence over PC knowledge skills.
I really want the players to learn about the game and the monsters, and apply that. I like skills to tell me how well you do something, not to tell me what you know or tell you what to do.
Knowledge skills, though, say that your paper man may know things you don't. Not how to do things you don't, or how to do things you know how to do but differently well, either.
This is especially true for Hidden Lore.
PCs always ask the same questions, in variations - how do we kill it, where are its vitals (more properly this is Physiology), does it take extra damage from attack type X or Y, etc. They're looking for a shortcut to killing it. Fair enough, they paid for that . . . but it's a problem in actual play.
I answer, but I'm looking at a full set of stats. If a person makes a roll by 0-2, what do I tell them? What do I choose? If they make it by 10+ with a critical, do I read off chunks of the stat block as someone else frantically writes it all down into the received, common knowledge of all PCs from now on?
Plus it means the skills take the place of player knowledge - people want to benefit from what they know, and what the PC knows, too. Or they get worried by meta-knowledge and don't want to use anything unless "my guy would know that." Those types of players tend to err on the far side of self-control, and say things like "I don't know that my guy would know trolls are vulnerable to fire." Yeah, by now everyone knows that.
On top of this, people want to use Hidden Lore every time - each time, they get more and more information. Do I feed more in, especially if the PCs learn nothing new from the previous encounter? Do I repeat the same stuff, and should I track that by PC? They don't really want old information, yet it feels like just because the players know that whatever new PC rolls shouldn't automatically add to the knowledge. If a Holy Warrior rolls and makes a good roll says you need to cripple all the arms on a Peshkali, does this mean the next time you run into Peshkali that Holy Warrior or someone else can roll, until eventually you've acquired most of the stats?
Plus, again, my approach is that you can use your meta-knowledge in this game. This is a best of both worlds - use what you know, and your PC might know more. If you memorized chunks of the monster book, okay, fine, but also your PC gets to prod me for reminders and information on monsters you've never heard of.
As you can see, I'm not in love with how it works.
Here is an alternative route.
What are we dealing with?
A Hidden Lore roll can be made as a free action to identify the creature. The GM rolls in secret. Success gives the common name and the type; critical success may provide additional information (identifying a sub-type, for example, and always giving any Vulnerability or Weakness or Achilles's Heel it has.) You suffer any Vision-based penalties, if appropriate. It's hard to I.D. what you can't see. A critical failure means you misidentify it.
To gain an immediate combat edge, take an Evaluate maneuver. You must first successfully identify the creature, as above. Failure to identify the creature means this automatically fails; a critical failure on the identification roll means you you can only or critically fail on this roll. You may do this at any range; roll against Per-based Hidden Lore, with penalties equal to range and any vision penalties. You may take extra time (p. B346) to improve your roll. On a successful roll, you gain a +1 to hit and to offset the penalties from Feints or Deceptive Attack for the rest of this particular combat. On a critical success, you gain a +2 to hit, instead. A failure means no penalty - you just don't sense a pattern or spot a weakness. Critical failure means a -2 to hit and a -2 versus feints and to defend for the same period of time - you're thrown off by mis-identifying the way the creature fights! This will not be obvious until the first time the penalty affects you. You must take the results of your roll.
You can pass along any information you gain with a free action to talk. You cannot pass along your bonus.
Such bonuses and penalties are specific to a specific type of creature - a peshkali or a wight, not against all demons or against all undead.
I haven't tried this yet, but I'd like to. It gives people a real reason to buy Hidden Lore for monster types, but eliminates a lot of my ambivalence. You still need to learn what works or doesn't work, but your character has information that can lead to direct combat bonuses.
+1 to hit and +1 to offset feints and Deceptive Attack, but it's not a bad bonus at all. Higher Purpose is still better, and surer, but using both can make for a killer combo. You can end up with +3 to all rolls, and a +4 or +5 to hit roll against a particular creature type.
It might be less effective for wizard-types. It's too much to give a bonus to spells (or inflict a penalty to resist), and might feel less useful for them to identify critters and then make it easier to hit them. I expect the wizards will squawk anyway - my experience is most people playing wizards feel they are very limited and very weak. That's not how anyone playing with, or GMing for, wizards feels.
I thought about making this bonus last the entire delve, but then I decided my players would try to game the heck out of that - "Let's go find a draugr, then leave it alone until we want to go after the whole bunch of them, let the Holy Warrior take a max-time Hidden Lore roll to get a bonus, and then we go fight them!" Ugh.
(Editing 7/6/2020 - Check the comments for Sean Punch's explanation of why the Hidden Lore skills work they way they do in DF, and my explanation of why I'm proposing a change based on a specific style of play used in DF Felltower.)