If you are new to 'Sins of a solar Empire' you may have come stumbled across a "there is no singleplayer!" troll on a forum somewhere. Although there are usually a number of people in this forum discussing multiplayer, there are also thousands with the game right now, creating and playing out their single player games, with no intention of ever playing a multi player game! Like Total War, or Civilizations, the game does not have a story-driven campaign, but this is not to be confused with no single player option. This mode of play is better known as 'Sandbox'
http://en.wikipedia.org/wiki/Sandbox_game
Sins has been recieving a lot of praise for it's single player experience. Here are a handful of quotes from major reviewers:
"Sins of a Solar Empire is an excellent single-player game" - Gamespot
"Sins of a Solar Empire has a large collection of custom-designed sandbox maps as well as a very powerful map editor players can use to create their own universes. Even if players never venture into multiplayer, there's plenty of gameplay inside the box." - Gamespy
"The single player gameplay is unquestionably addictive and will keep you awake for many late hours (thanks to how the AI does a good job keeping you on your toes with ferocious combined assaults or diplomatic offerings)" - Gameshark
"The dynamic and unpredictable situations that arise out of the open-ended campaigns are much more engaging than any scripted scenario. " - IGN