The more I play, the more I absolutely love the combat system. To me, it's two levels up from Witcher 3's combat (which I also love); having so many different spells, spell combinations, and enemy weaknesses to specific spells and/or combos makes it super fun.
I agree that the combat system is excellent and wonderfully dynamic.
My biggest gripe with the combat system comes from the inability to fit all spells into the quickmenu at the same time, something that is clearly the result of the system yielding to the restrictions of a console controller. That is a huge minus.
As to the unforgivables,
they are cool but mostly for show anyway. You don't need the killing curse to kill, your default ancient magic already explodes living beings. Or transforms them permanently to a chicken, or shrinks them to worm-size which you then squish under your boot. It was rather surprising that you end up blowing the troll in Hogsmeade to majonnaise in the very beginning.