I liked the Druid wildshape from 4e, where you changed your fluff but kept your stats. (I may be weird that way.) At higher levels you can add Fly or Swim or Desert Adaptation or Hold Breath to yourself. When every L3 druid from every corner of the world turns into Grizzly Bear as first choice, the mechanics are not working with the story.
Rangers should get bonuses from Favored Terrain and Favored Enemy, in combat and in exploration / travel. Hunters Mark should be a class feature, like the monster slayer's Ire is.
Sorcerer would get Spell Points, rechargeable per rest (half per short rest?). Each subclass should add themed spells - hhhhhhhhellllllo, Dragon Breath - and the base class lets you pick more. I would put Dragonblood and Elemental subclasses in the PHB.