All reactions should be toggle-able through their icon
(so you can deactivate attacks of opportunity for your mage who should rather counterspell).
Most reactions should be triggered automatically if toggled on because they would be too bothersome to activate manually
(like attacks of opportunity, protection fighting style or the shield spell).
The first possible reaction is performed, no choice to not perform it if the toggle was on (to not slow down combat).
Counterspell could be activated through a glowing "interrupt" button that appears during a hostile casting animation
(you may specify details in a second menu that pops up, hitting interrupt is the only thing that needs to be done within a short timeframe)
That seems like a lot of fiddling to save time. I know people usually roll both to hit and damage dice to speed up combat so I understand the mentality of "every second counts" but I'm starting to think at which point do we draw the line...
Triggering each possible reaction manually is probably overwhelming considering the huge amount of encounters per game session in a computer game.
In P&P, a fight might last an hour or more and you usually won't have more than a handful of fights per evening.
On a computer, we might do 20 fights per evening, meaning we'd have a reaction popup every few seconds, annoyingly slowing down enemy turns.
I can't imagine this would turn out fun.
A suggestion that might make everyone happy:- Reactions get their own small menu (doesn't make sense to mix them with abilities you can trigger during your own turn!)
- Each reaction has three settings: OFF - AUTO - MANUAL
- OFF means it's deactivated and never triggers
- MANUAL means you get a popup with 3 seconds to react
- AUTO means the reaction is triggered whenever its conditions apply
- Each reaction has a default setting chosen by the devs (AUTO for attack of opportunity, MANUAL for counterspell,...)
- In multiplayer, the game host could get an option to only allow the "dev choice" to make the game more fluid.
- Having all reactions in a separate menu would easily show you if you have enough viable ways to use your reaction or if you should learn an additional spell.
- Bonus actions could get their own menu, too. It makes no sense to mix them with actions if you need a different kind of "fuel" for them.
- A sperate bonus action menu would also show you clearly if you have sufficient viable ways to use your bonus action.