Very interesting, What I can add to this conversation is a bug? /wierd interaction with divine smite (maybe other smites to but havent tested those yet) has with GWM feat, normally if you kill outrite or crit a creature you can then use bonus action to strike again etc... Now with the new reaction system in place this scenario plays out 2 different ways. 1. if you set divine smite to automatically occur with out asking you to then you attack and smite the target, if the normal attack doesnt kill the creature and extra dmg from divine smite does then in this scenario you get your bonus weapon attack (as I would expect it to) now for scenario 2. if you set divine smite to ask you before actioning it ( basicly game pauses and asks if you wanna use it) and you choose to activate it and the creature is killed by the divine smite dmg then in this scenario you arnt awarded the extra bonus attack. Both these scenarios are executing the same attack sequences but just getting to the end result slightly different ways via the ask reaction mechanic, they should produce identiacal results in which i believe scenario 1 should be correct ( i could be wrong) but scenario 2 trips some were in the programming were it thinks its not part of the same weapon strike or something? maybe thinks is a different spell type? not sure, but hopefully larion gets it fixed as I like being asked to use resources before possibly wasting them, how ever not at the cost of an exta attack from the GWM feat as it currently stands. How I am playing it atm is if you think there is a reasonable chance to kill a creature using weapon attack plus divine smite then set it to automatically execute before attacking but if the odds are not in favour of killing then set it to ask, I shouldnt have to think this hard but the wierd 2 scenario things makes me do so when optimising dmg/resources understandably, let me know if you guys have experienced the same thing or if I'm some how missing something.
