IMO, all classes need to be tied to their theme/story more. There's also too much overlap.
Artificer -> They need to prepare all their items ahead of time, which is a slow proccess. They get X craft points, but can only spend a few of them each long rest in order to craft potions, bombs, imbue wands, program golems, magic item, etc..., which can also be given to allies. Items remain enchanted until used, or you disenchant it, which they can do remotely durring a long rest. If they die, it remains enchanted, which is how items came to be. Powerful if they prepared correctly, weak if they did not.
Clerics -> Mostly good, but could use a stronger theming with the spells. Pick 1 major and 2 minor domains. You get sub-class features and high-level spells from the major domain and low level spells from the minor domain. Add land druid domains.
Druid -> Combines ranger, totem barbarian, werewolf, 4e warden, 4e shaman, etc... into gish-y half casters that can buff themselves with nature spirits and shapeshifting. Flexible combatants can shift from speed, damage, defense, vision, stealth, grapple, support, or whatever on the fly (bonus action).
Paladin -> No spells. The only class with heavy armor and martial weapons. Oath abilities only trigger when you are doing oath-things (i.e. vengeance can smite someone who dealt him damage). Including things like oath of rage (beserker), and oath of leadership (4e warlord). Powerful when following his oath, weak without.
Sorcerer -> No preparing spells or spell slots. Instead, you have spell point and meta-magic to spontaneously build-a-spell. Includes bard with spontaneous build-a-song. Flexible casters.
Mystic -> Mostly good as is, but power points are short rest. Add the order of the fist (monk) discipline.
Warlock -> Mostly good, but could still use stronger tie to the story. Recharge spells by appeasing your patron. Reduce eldrich blast, and add escape options.
Wizard -> Mostly good as is, but allow preparing spells during a short rest. Somewhat flexible.
Fighter is just a bag of numbers, so he's gone. There can be a simple paladin oath for those who want simple guy with weapons.
Rogue (and bards expertise) only makes the DC's go up for everyone else. It can now be reduced by 5 across the board. Cunning action is fun, but not enough of a theme to base a whole class on.