yeah in the new Star Trek, it's just supposed to be understood as a kill setting. we aren't really sure how powerful the phaser is. Neither Kirk nor Spock get hit and the Romulans die like mooks are supposed to die. The Stun setting just drops you and presumably so does the kill setting. I go with the assumption that they don't act like Star Wars blasters... those were essentially bullets that looked like lasers.
couple of notes... I'm treating those Abrams phasers as having a whopping 300 charges (that's 100 stun shots or 20 kill shots) and you can treat the fast action of a phaser like the continuous beam feature (+2 to hit, +2 charges spent). Yeah. Phasers are terrifying. They should be. My only qualm is that they make PCs a little too vulnerable. There's only so much cover you can come up with or courage bonuses before getting hit at some point. I like the idea of some kind of "plot armor" being in place in star trek. Kirk, for example, doesn't get shot because he's Kirk darn it. The official Kirk has +3 Quickness, 12 health, and 6 courage. He's going to get smoked in a fire fight at some point.