Ultimately, this is a game, so the physics we use is not necessarily what you would actually experience in space. Some zero-g effects, like kickback from weapons and inertia when flying, are dampened so that the players aren't constantly fighting to keep themselves in control. On the other hand, some objects, like debris, will behave in a more realistic manner. More care has to be put into level design, since a player can easily get to any part of it, up or down. This also makes path-planning for the AI a lot more involved.
Space stations are the biggest part of the environment.
The player has access to both massive exteriors as well as interiors. Large domes and pods will contain multiple rooms and corridors and they will be attached to modules and arrays. Many of the domes and pods will have been designed for specific purposes, such as a mining dome, and the interiors will reflect that. Basic weapons such as the machine gun or rocket launcher will be augmented with specialty weapons and countermeasure weapons to be announced at a later date. Intelligence devices will be available as well as incapacitating weapons for capturing personnel or vehicles.