For games I don't take very seriously, like D&D or Fallout, I will often describe violent actions in graphic, over-the-top detail. For Fallout in particular, I describe scenes like you might in the video game series where heads, arms, and legs are often separated from the body by a judicious application of bullets. For D&D, if a player scores a critical or does a great deal of damage, I'll sometimes describe them or other nearby objects being sprayed with gore.
In a more serious game, like Call of Cthulhu or Delta Green, I still have graphic violence but it's a little more on the realistic side. Most of the time someone doesn't instantly die when you stab or shoot them, they struggle for life as it oozes out of them, sometimes crying for help from God or their mothers. I'll sometimes describe the smell of blood or other unpleasantness associated with death.