Crawford says it’s the biggest yet, with 7 classes (Experts: Ranger, Rogue, Bard; Priests: Cleric, Paladin, and Druid; and Monk confirmed), spells and weapon mastery tweaks, capstones back at lvl20 (epic boons will be pushed to another UA), and subclass progression reverted to the 2014 cadence after lvl3. Notably, rogues are seemingly getting another feature at lvl5 to make up for the fact that they get very nothing from their subclass between 3 and 9.
I think subclasses are more inline with variant classes in 3.5. You had a cloistered cleric vs cleric and they had 2 domains. You had the totem barbarians, the divine bard vs the normal bard. Prestige classes were far more transformative than subclasses and subclasses don’t feel the same to me in 5e.