A bit of rambling below:
I like the wrist-gun idea. Being on the wrist, the soldier is immediately ready for action, in the event the ship is boarded. It will need some kind of "safety" to prevent accidentally blasting your own station, or your neighbor. Firepower has to be controlled--you don't want to rip a hole in the side of the ship if you miss your target. In a battle scenario, it must have lethal force, so this would be the default setting, though MP type soldiers might have theirs set to a non-lethal force. Bad-ass appearance is important, but when not in use, it must leave the hand and completely free so that the soldier can perform his normal duties. Clothing cannot obstruct the weapon, or else the soldier risks frying his arm at the first firing.
If a projectile-type weapon (like a handgun, as in Battlestar Galactica) would need a means of simple reloading. It would need to use a magazine--perhaps a 9 or 10 round 9mm cal. The soldier would be required to carry replacement magazines on their person--checking with what the modern army or navy does now would be a good model.
If an energy weapon, then you need to deal with recharging. Nothing like phasers that last forever (like machine-guns that fire thousands of rounds without reloading). I kind of like the power that the wrist weapon from
Earth: Final Conflict had--but again, you don't want to rip holes in your hull by mistake.
Being far future, it should have sophisticated targeting capabilities, perhaps even detecting targets on the other side of bulkheads (how hard would that be to do, anyhow?) If you've been boarded, you want to take every advantage you can to eliminate the enemy. And really, the ONLY reason any soldier on a ship would carry a weapon would be to be prepared for facing the enemy in close combat. If there is no possibility of being boarded, they why carry around something that will do nothing but get in the way of your duties?
Yeah, a bit of rambling--maybe there are some ideas to pull from in there.