The blacksmith makes weapons and armor, of course, and can add sockets to items when possible. The mystic enchants items and creates magical implements like scrolls, potions, runes and charms. The jeweler creates gems, amulets and rings, and can also combine existing gems and remove socketed gems. Each artisan has a quest line and backstory and has skills that can be upgraded by the player.
A Blizzard game with crafting? It'll never work.