They screwed around with health pools a fair bit. While most are still buffed from the big S9 changes, (pre-venture), some heroes were reverted to 225 (down from 250).
Also new support, Juno, she fun and speedy.
Cuz of Juno, dive is meta (mostly D.Va and Winton). They nerfed d.va last patch but she still good.
There was another rank reset, so u can do comp placements again.
Main new cosmetics-related things are Mythic weapon skin (in the mythic shop), they cool but cost same as a mythic skin. Also with cosmetics, u can "try out" anything in the shop to see how it looks in the practice range without needing to buy it first.
Also new Push map, Runasapi (where Illari's from), and new gamemode Clash, which is a fast-pase 5-point looong map mode, which uses redesigned 2cp maps.
And das all that new... for the most part. Just play and you'll get used to everything.