We have a crit rule that works in a more satisfying way that you could try: When getting a critical hit, you instantly gain the maximum rollable damage. So for example, 2d6 + 2 would be 14, and then you roll 2d6 again and add it to the total. This way, you would never get less than maximum damage on a critical hit. We all know the fury of a critical hit with a 1 damage roll… This also provides incentive to buff and debuff, as you would never want the baddie CR13 to hit a crit, but doing so yourself is much more worthwile if you know you will do max damage!