Lengthy first post coming up, here's a few suggestions for the whole "Materia" system and some for crafting.

Removable, destroying materia
As mentioned before, it is a giant bummer to customize your favorite weapon and not being able to re-do that customization with better components found later on. Allow us to insert new materia by destroying the old in it's place.

Destroy weapon, keeping materia
Likewise, we keep on changing weapons, maybe we want to keep a materia we are really in love with, that fits our playstyle, or is pretty rare. Destroying the weapon to keep the materia is another good compromise when we just need to get better gear, and it eliminates some weapons from the market. More power to our Blacksmiths and whatnot, I suppose.

Don't give it a "Break if fail to attach materia"
We are already compromising with choosing what to keep, don't make "materia attaching" a stupid game of chance where it breaks our weapon or materia if we "fail" to attach it. Imagine me sacrificing my lovely sword to keep my even more so beloved rare materia, gained from an otherwordly Notorious Monster. Only for it to break when getting attached to another sword. BAH! Failing a synth is already incredibly punishing and counter-productive!

Materia Leveling
Leveling weapons, equipment in general, and skills is a rather common thing to do in MMO's nowdays. The reason is because having to nurture different aspects of your character is engaging and gives you a bigger list of things to do (reputation fits in this aspect). I would strongly suggest to give us ways to level up our materias, be it by grinding some form of experience directly from combat, or by a form of item infusion.

A Cap
With all honesty, you chose a hard-to-please demographic, catering to both casual and hardcore players... I would suggest merely giving a VISIBLE cap on the materias, in the case they do level. No invisible cap to get people complaining about. Just make it so after X amount of "EXP", the numbers change colors and the player is aware that that materia will no longer be receiving EXP. Another method is for the player to have to chose the (maybe one, maybe just a few) current "actively growing" materia so that they don't level them all up at the same time and have to swap from "actively growing" materia to "actively growing" materia after hitting the "cap". Making incredibly huge amounts of points required will only cater to the hardcore and discourage the casual, giving invisible tiny caps will only go unnoticed by the casual and enrage the hardcore who's been grinding it for hours and wasn't even sure he was on some "Materia Fatigue". You guys chose the target, you'll have to juggle with it.

Interacting Materia
I would like to suggest you make it so it's not just a number-stacking game. Making, much like in the original scenario, materia that by itself have no effect, that must be combined with other to enhance or activate. Such as combining some "enhancement-type" materia with a "base" materia so the base is increased in power, or maybe make it's power far more effective when fighting a certain type of enemy (birds, beastmen, etc.), or maybe make that materia affect all of your party in a smaller effect, for example, if the base increased MY "Cure Potency", it will increase everyone else's by a smaller amount.

Get creative, think TWICE before adding "VIT+1"
It has been mentioned before, Dex+1, Piety+2 and so on are not only easy, uncreative enhancements, they are all too uninspiring. Enhance individual skills too, things like this:

Quote Originally Posted by Biggs View Post
Don't just boost 1 or 2 points of dex or add plus 1 to evasion, give us something inspiring. When you call a system materia, it conjures up images of me infusing my breastplates with skills like permenant protect and shockspikes. Making my boots randomly have the chance to activate featherfoot at no stamina cost to me each time I am attacked would be the business.
Things like that, giving elemental damage to a particular skill (Fire damage on Heavy Strike, for example), making skills AoE (skills that weren't of course, like Concussive Blow) at probably a higher cost (more TP or Stamina, for example), lowering a specific skill's cooldown, or another's Stamina Cost, be able to grant your gear greater elemental affinities or, as mentioned by the Biggs there, permanent buffs, perhaps at a halved or lowered effectiveness, to not make the spells themselves useless. I'd have protect 24/7, but lowered on effect. Hey, at least I don't have to SLOT protect to use it now!

No Dumbing Crafting Down
It CERTAINLY needs fixing in many ways already pointed in this thread, but taking out progress bar really scared me. I'd like to see what exactly is being thought. I hope with all my heart you don't turn the crafting here into everywhere else- Click, watch, done. It would be meaningless to be a "full class" as an Alchemist if it has little to no interaction, like in every other game where I cook "50 roasts" by writing 50, clicking craft and literally opening my DS or PSP while it plays itself. It hasn't been said what will be done with craft system, just that the progress bar will be taken out, I hope it stays or at least it keeps being very interactive, proper to being it's "own class".

If anything I'd suggest you spice it up because it's pretty sad I have EXACT same interaction for all of my 50 ranks, with ALL of the Disciples of the Hand. There is no difference when crafting as a Blacksmith or a Carpenter, so as it stands, you CAN say "I enjoy Pugilist far more than Gladiator", but you CAN'T say "I enjoy Goldsmith far more than Alchemist" because they all play the exact same way in the Disciples of the Hand, as opposed to the Disciples of War.
I'd suggest checking http://forum.square-enix.com/ffxiv/t...s-to-Synthesis out, for a very good example.

Failing a Synth, not BREAKING a Synth
This needs to get addressed. Perhaps not remove synth failure entirely, but this is absurd. I am not even talking about the horribly damaged rate that has been pointed out by my other fellow poster (specially the OP), I am talking about the act itself of breaking a synth and losing everything (which has also been discussed, mind you). Hear me out here, how about instead of just plain blindly losing all your very hard earned Khroma Or-- I mean, incredibly rare and expensive items by turning to smoke on a failed synth, we just get a "bad grade result"? Say you are making an Iron Sword, and fail the synth, you turn out with a "Unfinished Iron Sword" or "Iron Sword -1". This Iron Sword could still be salvaged by being taken to a person with a rank higher than that required by the sword, perhaps by 5 or 10 ranks, with just A (don't make it an obscene amount of equally rare items, for Christ's Sake, it beats the purpose) item to "finish" the work, like an Iron Ore, or better yet, a simpler item like a Whetstone, maybe a -2 would need more materials (or of higher quality, ie. +1). With NO chance to fail because we'd end up in the same place, you are already paying your failure with paying someone for their services AND additional materials. If you really just don't want a giant influx of swords in the market for some reason just lower the material drops or increase required items to make them, don't just have it disappear because Lady Luck wasn't home tonight. This is just a random idea, but I suppose it helps the economy AND frustration a bit, while also creating some more player interaction.

I apologize for such a lengthy post, thanks for taking your time to read it.