Everyone line up, and we march at each other, and shoot, and reload, and shoot, and reload, and shoot, until one side is dead.

... didn't that sort of thing go out of fashion in the 18th century?

Technically, the ships shown in GCIII's battle viewer continue to maneuver even once they have closed with one another. However, since maneuvers have no impact on whether or not the ships actually get hit, it's basically just window dressing.

Also, don't be so dismissive of 'lining up and shooting.' The battlefield environment for a space battle lacks any kind of cover or terrain which might provide an advantage to one side or the other based upon how it gets used, and the ships involved are, so far as we can tell, incapable of performing maneuvers which could materially affect the hit rates of the various weapons. Weapon systems have the ability to fire in any arbitrary direction, and defenses don't care about the direction from which an attack comes or where on the ship the attack lands. Additionally, weapon accuracy is independent of the range to the target. The only type of maneuvering that has any value under such conditions are the maneuvers which keep longer-ranged ships out of range of shorter-ranged ships, but that's still 'line up and shoot the other side,' the only difference being that one side is also supposed to remain out of the range of the other side's weapons, and I'm pretty sure that one of the developers (maybe Frogboy?) commented in another one of the threads about the combat system that not coding that tactic into the game was a deliberate choice to prevent missiles from being a vastly superior weapon system.

Moreover, that 'sort of thing' did not go out of fashion in the 18th century, unless by 'lining up and shooting at one another' you mean a complete lack of any understanding of the value of maneuver (which fails to describe just about any set of tactics for any battlefield on land or sea or in air in any period). Armies continued to line up the infantry to shoot at the opposing army's infantry well into the 19th century and did a little of it even into the First World War (early 20th century), and there are probably circumstances where they'd still do it today. Engagements between big gun warships continued to be essentially that until big gun warships went out of style (and it's not clear to me that engagements between modern missile-armed ships would really be all that different, either, seeing as there's a distinct lack of cover except quite close to the shores, and there's not a whole lot of positional advantage to be gained from maneuvering when the weapons involved are missiles that at worst only need to be pointed in the right general direction).

This EXACT same question came up just a few months ago and it got pretty nasty.  The question still stands though why we can't issue some limited pre-battle commands for fleet dispositions or limited targeting orders (such as "stand off" or "close to enemy).  Combat in this game is woefully shallow which is a shame considering how much better the game has gotten since release.  Hopefully it will get some attention later on down the line.