I have played the basic game for years now, the diplomacy is quite basic the usual NAP, Aliance swap money, swap research points , there is no colony management aside from balancing production/infrastructure/income sliders. the setup is geared towards a more fluid multiplay but it don't have the level of detail I like for single player which is what I do most of the time.
Good points for me of SotS
unique travel methods for each race
"realism" of fixed firing points as opposed to the omnipoint firing of the likes of MOO2
Semi-random tech tree for each player
Quick to setup a game
Bad points for me of SotS
Basic Diplomacy, it lacks the ability to establish trade, swap research and you can only do one thing at a time
Basic Colony management, no building aside from ships
Only space combat is considered nothing about ground combat so the only way to conquer is to wipe out the population of the target planet
No species Customisation, MOO2 was awesome in this respect with a huge number of stats and abilities to fine tune.
I'm not saying SotS is a bad game, in fact is has many things in its favour, what I'm saying is that It lacs the depth on the civilisation management side for me to fully enjoy it for more than a few days at a time, as a multi play it is probably a blast and i imagine a lot faster pace than is the norm for 4x games. What extras does the expansion add?