Star Trek is one such RPG setting.
Each player character in a Star Trek RPG, unless otherwise instructed or prohibited not to, carries as their common sidearm a cell phone sized energy emitter that causes targets, once hit, to vanish. It is a 'go away' gun. Someone is hit, they 'go away' permanently.
This is, in no uncertain terms, really, really powerful. I know the various officially licensed and even some of the less than official Star Trek systems give detailed charts to determine the damage of a Phaser on different settings but really it all boils down to 4 'Conditions...
Stun Setting - You are hit, you are unconscious.
Heat Setting - Used to heat up rocks or weld or burn through doors.
Kill - You are hit, you are dead.
Disintegrate - You are hit, you glow briefly, you go away.
Now this isn't just the good guys we're talking about. This is the basic firearm of the setting. The Klingons, the Romulans, the Gorn, all of them have weapons that turn you into vapor in seconds.
This presents players and their characters with a very different combat dynamic than they are used to in most other games. It may take one or two sword swings to fell an Orc, a couple of rounds to take out a spy and a superhero will blast his opponent with heat vision and lay down a few 10 ton punches before the fellow is merely knocked out.
That is not what is going on here. This is one successful hit, one enemy gone. This is like real life combat where one bullet can kill a person.
So what is Adam getting at with this post? Simple. Armed combat in the Star Trek universe is quite unusual from what you may have encountered in other games. There are numerous ways to handle it but, in my opinion, only one overarching way that keeps the feel of Star Trek.
Perhaps the most common and easiest way to handle the power of a Phaser, Disruptor or similar weapon is to depower it. Assume, as often they seem to do in post-TOS Star Trek, that the default setting on the weapon is similar to a Blaster, simply a beam of light that hurts and nothing more. This is done without much fuss or muss by altering the amount of damage caused on the aforementioned charts most Star Trek RPGs love to give us. This will ensure longer firefights and a kind of action movie approach to Phaser combat.
Another way to handle it is to limit the charges on the weapon. The idea is that the Stun setting draws much less power from a Phaser or Disruptor's power cell but a Disintegrate setting draws quite a lot. There is some precedent for this in the show, although it's never clearly stated how many shots will drain a Phaser.
My last suggestion is both the most Star Trek-like and yet perhaps the hardest to convey to most gamers. This final idea is one of theme. Star Trek is essentially 'Wagon Train to the Stars' and the firing of a Phaser is like a Cowboy drawing his gun or even, a Samurai in a Kurosawa film drawing forth his katana. You do not draw your weapon unless you are prepared to fire it and you do not fire it unless you are prepared to kill somebody.
This respect for the weapon and what it can do often leads my players to set for Stun much more often than Kill or Disintegrate. Enemies need not die if you don't have to kill them in a Star Trek setting. Not every opponent need be vaporized. Disintegrated opponents don't reveal their plans or tell you how to deactivate the world-destroying alien satellite. No renegade starship captain or mad scientist was rehabilitated or stood trial for their crimes in the form of vapor.
At the same time, it always Starfleet officers to walk around with a bit of a swagger. Much like the old west, these are individuals who may not want to wipe you off the face of Gamma Arcturus V but they will if they have to. A Starfleet officer has to do what a Starfleet officer has to do...
More on combat in the Star Trek universe and what it means to gaming there coming up in...