My description varies on the nature of the combat. Your typical fight with standard enemies rates pretty standard description, unless someone rolls a critical, in which case I step up the gore a bit. In more cimematic fights I describe things a bit hyper realistically, reaching almost Wuxia levels. In some combats, those that I want to really matter to the players later I become very visceral, really describing the damage done to themselves and their opponents. In those instances where someone has commited murder, I describe the event with as much detail and gruesomness as possible, so that it really sticks with them. Now I should say this changes with the PC, the one assassin player I have had in my games had reached the point where I described his actions very simply and matter of factly, since death was no more notable than eating to him.