Edit: Regarding Reactions. It has been stated that the Reaction system isn't working, but Larian is figuring out how to best implement it with regards to reactionary spells (like Shield or Counterspell) and other such abilities.
I think they stated that it wouldn't work, prompting players if they want to use their reaction point after every enemy movement action would cause the game to slow down. There might be ways to do it which would work okay, but they've (at least in this build) scrapped it, reactions are only used to take an attack of opportunity. Spells like feather fall are cast using your action (or possibly bonus action, I didn't quite see) and have a duration.
Other DND games have done this as well, where shield was a temporary buff to AC and negated any magic missiles being cast, but those were in real-time and you could cast them in response to seeing an attack coming. So we'll have to wait and see if the reaction spells still work well after being amended.
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I don't mind the initiative change, original sin 2's multiplayer had an issue with waiting for other players to act, having simultaneous player and enemy turns makes sense.