I don't care what exactly they choose as long as it's weird and emerges as a result of giving real thought to the physics considerations of different situations. Since we will have spinning stations, free-floating zero-g environments, zero-g with magnet boots, and planet surfaces of varying gravity and atmosphere, there should be weapons and tactics which are appropriate in some situations but utterly disastrous in others.
Projectiles for example would be a terrible choice inside of spinning stations because their trajectories would skew all over the place depending on whether you were shooting with the direction of rotation, against it, or across it. But they should still let you try. Meanwhile you'll have to use a combination of unusual firing stances and shoulder-mounted thrusters to compensate for anything with recoil when you're in magnet-boot mode, and firing anything with recoil while floating in zero G would be right out. As for what kinds of weapons you'd use on a 6x gravity airless planet (assuming a human can even survive there)? I dunno but it better be lightweight.
What I specifically DON'T want is a solution where you have all the usual videogamey FPS weapons and they behave exactly the same in every situation. Handwavium should never be used as an excuse to make something more generic and cookie-cutter. By all means, have an SMG, rocket launcher, railgun, etc; but make them behave differently in ways that respect the fiction of the game.