OK, before I let myself get distracted responding to someone else, again...
FOOD MECHANICS!
I want to use this post to work down from these abstract high-level concepts I am talking about into the small-bore, so as to give people a better understanding of the argument I am making.
To start with, however, I want to go back to make positively clear on the definition of the terms I am using.
Aesthetics are the reasons why we play games. If you say that the thing you most enjoy about a game is the sense of the hugeness of the game world, and wanting to look around it and experience just the fun of looking around such a huge and varied world, then what you are talking about is the aesthetic of Exploration - the joy that comes from just plain discovering new places in a game. This is an entirely different aesthetic from Challenge - when the game is fun because you enjoy the actual act of the overcoming of the obstacles the game throws at you. (Again, if you play a game like Bejewelled or Sudoku, those are games that are entirely based upon Challenge - you play them because you find the very act of overcoming their puzzles to be an enjoyable act.)
Mechanics, the way that the game is programmed, exist to deliver upon those aesthetics. Because the purpose of mechanics are to deliver to players different aesthetics, which are the things players can enjoy about a game, you can judge a mechanic's effectiveness by how well it delivers upon its intended aesthetics. And yes, mechanics can deliver more than one aesthetic.
Core Gameplay Aesthetics are the biggest reasons why you enjoy, and ultimately, play a game. Most games only have 2 or 3 Core Gameplay Aesthetics, and those are the reasons you play them. Sudoku, to use a simple example again, is based upon Challenge and Abnegation - if you enjoy playing those at all, it is because you like having everything reduced down to simple, logical steps that are easy to understand and "zone out" over (Abnegation), as well as the little joy of feeling clever for being able to deduce the exact numbers you need to fill out the boxes (Challenge).
So, onto the discussion of the food mechanics introduced in Book II, which are a smaller-bore, more concrete example of a rather independent mechanic system in the game, which makes it easier to dissect and discuss in terms of aesthetics in the absence of other game mechanics.
If I were to rate how the mechanics for food work currently, honestly, I'd give it a "fair" rating. The mechanics actually do provide some positive aesthetic to the game, even if they aren't providing the Challenge that the game claims they are providing (along with experience point bonuses), but do help present some Fantasy for the player in the sense that it helps complete part of the notion that you're really out there camping, making do on rat meat and water skins in the desert.
The thing is, it doesn't do this terribly effectively. There's no real challenge to feeding yourself even from the start, when you can just buy all the food you really need for pennies and get infinite water at a well, and you are not really ever sent to places where you're really, truly challenged to have to scrounge up food or given the feeling of being a real survivalist.
Challenge and Fantasy are the two aesthetics I can see most easily satisfied with such mechanics.
Games like NetHack involve food for challenge - it's actually quite dangerous to just try to find something to eat in that game; More than a few adventurers wind up dying just because of botulism from some food they took a risk eating. Need for food pushes you onward in the game, encouraging actions that involve risks you otherwise would not take because you are in a press to get access to safer food.
However, the game that I think best incorporates hunger mechanics into Challenge (and Fantasy at the same time) is the game
Lost In Blue. In that game, you play as a shipwrecked young adult on a deserted island who has to survive while exploring the island for some way to contact civilization and get rescue. Food is the whole core of all the challenges in the game - you are tied to a base camp you generally must return to every day for food preparation purposes (and sharing what food you have gathered with fellow survivors) and so how far you can go is generally limited by your need to gather more food and bring it back within that one day. The various block puzzles and hurdles in the path to exploration are all fairly easily solvable with time, but time is hunger in this game, and as such, everything relates to how efficiently you can gather food.
However, basically all the game's enjoyable moments tend to revolve around the gathering of that food, as well, which is why it's such a good Challenge aesthetic. You start out merely running along the shoreline looking for shellfish to sustain yourself on, or sampling mushrooms (where what each color mushroom does is randomized on game start, so you can't know ahead of time what each mushroom actually does until you sample some - and one is the highly beneficial "caffeine 'shroom" that temporarily slows down depletion of the energy meter, making dashing or shoving heavy objects free for a limited time,) but you can eventually fashion crude spears to spear fish with, fishing rods, cages for catching wild animals, or even bows and arrows to hunt boar or other large game.
Building food systems for Challenge, however, tends to require that you genuinely build the game around making it seriously
hard to keep yourself fed. (Making food so cheap and easy to stock up on in the first place severely undermines that challenge. Worse, the whole tier 1 cleric spell that lets you summon food infinitely for free kind of blows a hole straight through any conceivable challenge there.)
Alternately, you can produce a system where mere sustenance is not terribly difficult in and of itself, but where there are obviously superior foodstuffs out there that do require overcoming challenges to secure, and therefore can force an enjoyable challenge to try getting. (For example, if you could keep yourself full for five straight game days and get a permanent +2 to Strength if you ate a Dragon Steak, it'd be worth going to crazy lengths to try to get it.)
Fantasy is also an aesthetic that food systems can deliver on quite well - and which doesn't necessitate quite as much recalibration of the rest of the game mechanics.
Fantasy is the aesthetic of being able to enjoy the sense that you are actually transported to some other living, breathing world. "Realism" in a general sense helps to lend Fantasy (ironically enough) to a game, and the realism of having to actually eat does help, although it has to be presented in the game in a way that is actually meaningful in order for the fantasy to really sink in.
Like with challenge, there isn't really much fantasy added to a game when you just have to go to the local tavern, spend some trivial amount of money for food, and then max out a food bar, or manually have to punch a button to keep a hunger meter down.
Building up the fantasy requires that you do things in such a way that it gives you a better sense of you
being the character, and an occasional stop at a supermarket and punching the right-click on a stack of rat meat doesn't really give one the sense of being a wild outdoorsman.
Even though this isn't actually directly food-related, I'd like to point to the Skyrim mod
Frostfall for a wonderful example of how to incorporate Fantasy into a game. In this mod, the coldness of those frigid mountaintops or glacial waters actually starts to come to life by actually introducing a mechanic for your character getting cold and freezing to death unless they take steps to preserve their body heat, such as making sure they only sleep in colder climates after building a fire and building a warm tent.
Skyrim is a game that already has a good deal of effort put into creating what could have been a wonderful fantasy that was seemingly left on the cutting room floor mostly to help sell the game to the people who just wanted to bash things, but where the modding community allows for a great deal of Fantasy to be put into the game.
The game also has plenty of ways to make you feel like an outdoorsman - you can hunt deer, catch fish... and don't actually need to eat them without having to mod it in.
This, then, is the problem of how food is handled in the game as it stands - it doesn't really do anything but require the player occasionally click on a food item, and doesn't really provide players with any sense of being an explorer or surviving harsh conditions (even when they are eating quite disgusting things) when they do so.
What could be done to remedy this is to help create those conditions of either Challenge or Fantasy. In fact, you could even include Expression if you were to use some of those Origin or Axiom in this.
Take, for example, if there were a player character "Mood" or "Patience" mechanic, as well.
This could be a bar that represents how many tedious or disgusting things that sort of character would be willing to do. For example, wade through filth, or, more importantly, to do things like constantly search for either traps or treasure or for roots or berries, or to do things like go out and chop wood or make alchemical products or set traps or any other non-combat thing that gives the player an advantage, but takes up character time.
This, then, is like an "MP" bar for using non-magical skills, and it could be recovered by doing things that are comforting to the character, such as eating good food and drinking things they find comforting.
This comforting thing could be dependent upon the type of character - a nefarious character might love the finest wines to relax, or enjoy killing things or making them suffer, while a druidic character might refuse all alcohol, and get their enjoyment from drinking herbal teas (which may be gathered by using an herb-gathering skill that, itself, may hurt the mood bar).
Food quality in general can also be mood-affecting - you're not going to have a satisfied character (and if that does things like drop the character's attentiveness towards traps, or disallow some skill uses if they are in a nasty enough mood, then that's a problem...) if you feed them nothing but a diet of insects and rat meat, but they'll be just peachy on a diet of constant steak and potatoes.
It's also worth pointing out that you should be able to take away the micromanagement of some of these mechanics, so that they don't particularly wear on a player. In particular, I find it kind of silly that a character seemingly can't eat while quick traveling on their own without you manually telling them to. One of the older Oblivion food systems I remember included a special "mess kit" container that let you just dump the food you wanted to eat, in order, into the mess kit, and when it was time to eat, you just ate the top thing in the list. Simply queuing up waterskins to be imbibed automatically, especially when on the road, is a way that lets the player not have to spend so much time specifically looking at a food bar and manually punching an "eat" command.