New Combat Mechanic

[The Kwisatz Haderach]

I was thinking about ways to make combat feel more exciting. Maybe a little more theatrical. I’m toying with the idea of dropping the static 10 for AC and instead having everyone roll for their defense and add their modifiers. Maybe make it so on a Nat 20 the defender gets to make a Counterattack, and on a Nat 1 the Attacker gets to make another attack. I feel like this could make combat a lot more exciting. Has anyone toyed with a system like this? If so, how did it go? Does anyone see a reason why this would be game breaking one way or another?

[DungeonmasterCal]

I don't see it as game breaking but it could slow down things a little bit. I've made some changes to combat in my houserules, which does slow combat, but my group likes the changes so we kept them.

[avr]

Rolling for defense is an old optional rule. It makes combat more swingy but not so much it breaks things. Adding extra attacks on natural 1 or 20 would make it slightly more so.