To improve crafting systems, we need to understand how they work. The first step to that is being able to describe and categorize them. After several weeks of mulling over crafting systems in everything from MMOs to survival games, I've settled upon some simple definitions that should describe nearly every crafting system out there:

Availability of Materials:

• Unlimited: The player will always be able to gather more materials; the only restriction to how many materials he can gather is how much time he devotes to it. These crafting systems are akin to Quest Logs: a series of goals to accomplish. Most MMOs and open-world games' crafting systems fall under this.
• Limited: The game imposes restrictions on how many materials a player can gather, either by limiting the amount of resources or how much time a player can devote to gathering them. The player (usually) has to give up making B to make A. These crafting systems are akin to Moral Choices: decisions to make between different options. Most roguelike and strategy games' crafting systems fall under this.

Range of Product's Quality:

• Uniform: All of the products of a crafting recipe are the same; there is no variance among them. WoW is an example of this: each Handstitched Leather Cloak is the same as every other Handstitched Leather Cloak.
• Tiered: The products of a crafting recipe can be split up into a distinct number of variances, often with obvious "best" and "worst" results. Items in the same variance are exactly the same, but differ from items in other variances. Final Fantasy 14 is an example of this: the result of any crafting can either be Normal or High-Quality, with High-Quality having better stats.
• Variable: The products of a crafting recipe cover a large range of stats, usually determined by a math formula. Few products have the exact same stats. The Elder Scrolls series are an example of this: a product's stats rely on the creator's stats, traits, and buffs, with no limit to how powerful crafted items can get.

Quality Determinants:

(Crafting systems with Uniform Quality Ranges don't have these.)

• Material-Based: A product's quality is affected by its materials' quality. In these systems, the quality and traits of the materials are important. Final Fantasy 14 is an example of this: High-Quality materials increase the odds of the product being High-Quality.
• Stat-Based: The crafter's stats (and his equipment bonuses) affect a product's quality. Crafters with high stats create better products than crafters with low stats. The Elder Scroll series are an example of this: high Alchemy/Smithing/etc skills mean more powerful potions/weapons/etc.
• Skill-Based: The player's performance on a minigame affects a product's quality. Atelier Sophie is an example of this: doing well on the crafting minigame increases the stats of the product and gives it extra effects.

Example Categorizations:

• WoW: Unlimited Uniform
• Final Fantasy 14: Unlimited Tiered Material/Stat/Skill-Based
• Elder Scroll Series: Unlimited Variable Stat-Based
• Atelier Sophie: Unlimited Variable Material/Skill-Based
• Thea: The Awakening: Limited Tiered Material-Based (could also be Limited Uniform, assuming you treat each material combination as a separate recipe)

Appendeum:

• You could argue buying/selling items is closely related to crafting systems, with coin being the only material for a wide variety of "products".
• I initially thought of adding a categorization for whether recipes required specific items (1 Iron Bar, 1 Cedar Branch) or any item in a similar group (1 type of Metal, 1 type of Wood), until I decided recipes that accepted similar items would have Material-Based quality determination instead.
• The difference between Uniform systems and Tiered Material-Based systems gets a bit tricky when arguing whether each combination of materials should be treated as a separate recipe. My current thoughts on this is that asking for a type of item, rather than a specific item, encourages different behavior from the player (more experimentation, less filling-checklist) and thus should be categorized differently.
• I debated whether the chance of wasting materials on a failure was important for categorizing a crafting system. I ultimately decided against it, since you could (potentially) treat it as a Tiered system (with the "worst" tier being the one where you don't get any product at all).

Thoughts?

Really nice analysis! As someone who ALWAYS checking out crafting systems within games (probably to a fault) I find this really interesting.

Couple thoughts:
What do you think about games that have things with slots for mods? Yeah you're not making anything from scratch but the mods can be limited resources. Is that crafting?

You mention time in a number of places. Personally I would break up availability of materials into object limited/unlimited availability and temporal limited/unlimited availability because they can have very different implications for gameplay IMO.

This is really cool! Don't have much to say besides thanking you for your time in doing this. You should try to add this to the Wiki. I would definitely be for it.

My initial thoughts is no, slotting mods is more similar to equipping items in extra equipment slots than crafting.

And I debated breaking it up into object-limited and time-limited, but I decided against it under the belief the end result (player making tough decisions about what to craft) was similar enough.