I think that a good ideain this case, for Brink, is to look at how Medic is used in Team Fortress 2 give their own unique twist to it. maybe that will be how the buff gun will work, or whatever the buffing agent will be. also if your getting Brink, Spread te word everywhere, and if you are gettin it for XBL put Revolution on your profile
Well, what we know so far about medic buffs is that, like TF2, you can give people more health than their normal maximum--but unlike TF2, it doesn't decay. The limiting factor is that you can only buff a certain number of people. Unlike TF2, you can buff yourself, but it takes extra energy, and you don't get any points for it. Unlike TF2, healing and buffing are different things: you can use energy to heal people instantly to their maximum, or you can use energy to increase their maximum health for the duration of their current life. You can also revive people who are incapacitated and haven't respawned yet.
The biggest TF2 medic idiom is the übercharge, which is a mechanic Valve included to break stalemates. Medic doesn't get that in SD games, but they do have the same firepower as everyone else to make up for it.