It's a classic class, but still -- elves and dwarves are classic, I'm not including them. And druids are worse than those two, which I exclude out of simplicity and unity of theme. Druids, I have problems with. Not the mechanics as such, but philosophical. The philosophy of druids in D&D is -- not the philosophy of people who actually live in the wild. It is an urban sentiment, and an urban sentiment in heavily urbanized societies. Even in the height of the Roman Empire, the non-urban ideal was Arcadia -- pastoral, filled with shepherds and sheep, not wild. Even in the early 19th century, there was the view that wild scenes could not be beautiful -- picturesque, yes, sublime, yes, but for beauty you needed signs of human habitation.
People actually living in the country were deadly practical when dealing with the wild, because starvation lurked if you weren't. At the very least, a druid would worry about human suffering as well as "natural."
Besides, I want a monotheistic world. Revering nature does not fit. Though a class could venerate the single deity more heavily for the glory and wonders of creation that other priests did, and worry about things like watersheds and firewood. The way most RPG worlds are really thinly veiled modern worlds -- obviously not suffering massive infant mortality and regular famine -- would help introduce more modern views as well.
And I'm NOT going to call them druids if I have them.