2D Space-Highly, hideously, completely adverted. Space has three dimensions, and they try to use all of them. Warships are built to have weapons pointing in the major directions (or at least have armor in those directions), and there have been space battles where two ships have been rotating in three dimensions and moving in another dimension.
A great game to simulate this effect is Squadron Strike, which has 3D combat in all three dimensions.
(For those curious, just about everybody’s ships use Mode Two (aka Asteroids) movement, while Griffins use Mode One (ships fly like airplanes) movement. There may be ship sheets posted at some point.)