you start out with one planet.
The campaign map is always the same (bit dissapointed in this, i dont think it would have been that hard to randomly gen one since its just aload of planet icons connected by worm holes.)
You still need to unlock stuff by winning battles in regular GSB
You cant do anything interms of management of planets you conquer. Planets come with facilities that produce 4 things (i think its just 4), factories = finacial income, acadamies = crew income, repair facilities = repair (at a cost, you pay per ship), ship yards = construction. Most planets have one or two of these facilities.
the enemy ai isnt strictly playing the game you are. As far as i can tell at the start the game assigns all the planets to differing empires. WHen you attack a system, the game looks at the value of your fleet + possibly the whole strength of your empire, then downloads a fleet offline (either designed by cliffski or a random player of the game) and fights you with it. Once this fleet is downloaded it stays in the game until destroyed. Every now and again they attack you, either downloading a new fleet or moving an existing one.
Planets can rebel if you dont maintain a fleet there.
my personal opinion: if youve got GSB get this expansion, if you wanted GSB and never got round to getting it, get it and get this expansion. if you played the GSB demo and didnt like it much, dont bother with this, its not going to sway you. This expansion brings some longer term goals and narrative to your battles, but the campaign map itself wouldnt stand up as a game, and doesnt bring much tactical diversity. Partly because until you invade a system, you have no idea who owns it, what fleets there etc, so theres alot of trial and error. My game strategy will probs improve tho, might start designing scout ships.
Also, its hard. Ive been playing on medium, two campaigns, im getting hammered in both, some people are much better at designing fleets than me, and to progress, you've got to win your battles with very minimal losses, as the ai will counter attack (it isnt resources restricted because it isnt playing the game as you are). Also the game autosaves, so you cant save scum.