The one thing that my friends and I still talk about was the SWG crafting system. It's been the best of the lot. The whole concepts of materials having inconsistent quality and that the quality could allow you to produce good and bad lots of the same item, or optimise for one attribute over another really set them apart from anything before or after. It was the sort of thing that made a crafter playable as a long term character because there was so much variety and constantly having to stay on top of things, compared to the grind of combat characters.
The key elements in human thinking are not numbers but labels of fuzzy sets. -- L. Zadeh