Personally depend's on "why" the game has crafting.
In my own opinion I enjoyed the Crafting from Monster Hunter Freedom Unite, because it has a purpose, though do not get me wrong it could have a lot more added to it, in the way of diversity.
worst crafting system I have seen would have to be WoW, I didn't see a purpose in it what so ever...
If I was to make a crafting system that would keep me coming back, it would have to not be based on a recipe system but rather random material's are flung together to give you a chance at making X-Sword. though if you have a specific amount of one mat, it will make X-Sword become the Hyper-X-Sword.... (excuse the naming)... I am not putting this across very well.
I will go see if I get note this down and come back with a proper explanation XD