The categories sometimes don't make much sense but that isn't something that bothers me while I am at the table running an game.  The thing that causes me problems running Pathfinder (only game in town around here too) is the way the categories interact with knowledge skills.  You need the right skill to try to identify something you encounter.  This combined with the willy nilly arbitrariness of the way things are classified creates some confusing and annoying situations.  What skill do you need to identify this thing again?  Knowledge:nature?  No, it's a magical beast.  You need knowledge:arcana.  It's an aberration?  Sorry, I mean knowledge:dungeoneering.  No one has that?  You don't know what it is.  No metagaming now.  It's just a pain in the ass.

I guess I should note, that I, all Cons taken into consideration, till come down in favor of having creature types in the game.

I love having Weapons of Dragon/Undead/Shapeshifter/whatever-laying, I like having Spells and Abilities detecting only certain beings. I am looking into adding abilities and Spells that make the divine/arcane magic split meaningful (for example, adding monsters with divine magic resistance, divine only counterspell, abilities that only affect arcane caters or arcane vulnerability). I want to add some mechanical effect to alignment (for example, when visiting outer planes).

I like cathegorisation in game design, is what I'm saying.

I guess my issue is that such game elements are far to often designed to be creative straightjackets, when I want them to be tools I can use to anchor a homebrew setting in the rules.

This has been a pet peeve of mine as well and I agree with everything said here. 5e by far has the best type system in that types don't determine combat statistics. There are still flaws as you have noted. Why can't types be more clearly defined? Why can't creatures have more than one type if it makes sense? How do you categorize spiritual entities that are not celestials or fiends or undead? Creatures from real world animism and occultism are a good example. Where does a manifest dream or river spirit fit in the type hierarchy?

For me, having categories is fine. Especially if the categories exist mostly as 'flags' for special effects (such as "weapons +X, +Y vs. _____"). Where 3e erred, and supposedly 5e does not follow, is saying, "oh, this creature is a _____. Therefore it should have d8 hd, attack progression of 3/4 HD, good saves in Reflex, and 4 skill points per hd." That created all sorts of problems in exchange for very nebulous benefits.
For example, undead. Undead are an iconic D&D type of monster, and plenty of class abilities and treasure types are dependent on knowing whether a monster is or isn't undead. For that reason, an undead flag is rather important. On the other hand, undead can be very different, and fill very different roles--from unintelligent skeleton to genius lich; slow moving wall-of-hit-points zombies to assassin-like special-effects wielding ghosts and banshees; from the incorporeal to the nothing-but-the-corpus. What are all these creatures doing with the same attacks, saves, etc. (even more than the rest of the creatures in 3e, which at least modify hp based on constitution)?

It looks like you've got a lot more categories, used for a lot more things than in the old days (when for instance the ranger's "giant class" list was just for the ranger's combat bonus).

I see the likely background of that as a desire to standardize a bunch of categories -- e.g., 'Giant' means the same thing in a ranger class description or a potion write-up -- that could be used to inform designers' game-balance considerations for magic items, spells, 'feats' and so on. (Of course that falls apart if the monster mix changes.)

Quote from: Doughdee222;866186There is something inherently buggy in the logic of it. I can imagine a sword being magical and thus causing extra damage to something. But then why would a sword decide "This flesh I'm slicing through is humanoid, I'll do even more damage than if it were a bear."

This is an emergent phenomenon of basic laws of magic such as contagion, sympathy and True Names. The paradigm is idealistic, not materialistic: magic taps the 'real' world of ideal types and essences ('substances') to affect the dependently apparent world of material ('accidents').

All this probably makes less sense even from a magical worldview when it's not set into the context of any such worldview that has ever actually been widely held -- or even one made up for game purposes but informed by some such --but instead is just slapped together in terms of a game abstraction with no reference to folklore and esoteric tradition.