Pro Diplomacy used in a smart way
Factions you play against can send you quests that may affect your relationship with others in the match. By taking on these quests, or even downright refusing them, your standing with the respective faction will change, causing a rippling effect that will increase or degrade your relations with others. Thus you must choose whom to aid and who to shun in an effort to create a strong alliance. This diplomatic depth of strategy can greatly change the outcome of a game depending on the strength of your alliance and military, as it is only as strong as your opponent is weak. And there is nothing stopping them from forming an alliance of their own.
Pro Leisurely real time combat
With the large scale of the game, you can control many fleets in several solar systems, which, on easier difficulties, allows for a leisurely pace to play. This makes the game a worthwhile, relaxing and semi-stress-free strategy title played on a grand scale.
Con Steep learning curve can deter casual players
While the game is one of the slower Real-Time Strategy titles, there is a huge learning curve that can wreak havoc on fledgling players. With some research required in order to colonize certain planets, researching use of larger fleet and capital ship sizes, to maintaining a thriving economic civilization, it will take many, many matches before players feel knowledgeable and skilled enough to play on larger maps or even against more difficult AI. With no true Single Player to speak of and little way of help in terms of tutorials, you must play in order to learn, sometimes using trial and error as a way of making progress.
Con Slow-paced logistics and combat necessitates situational awareness
Sins of a Solar Empire: Rebellion is a strategy title on a massive scale, with players able to colonize multiple solar systems in any given match. Due in part to this scale, there is a perceived slowdown in gameplay; lengthy building construction, minutes-long research and slow unit movement.
While the game, at its heart, does appear to be slow (and sometimes is), awareness of your surroundings is paramount. With fleets sometimes taking minutes to arrive at a destination, and defensive structures quickly falling to a massive fleet, it is easy for players to move out of position allowing key worlds to become targeted and lost in enemy incursions if they expand too quickly.
However, not expanding quickly enough can halt the player from building up a fleet capable of taking on an enemy, or pirates head-on. In essence, you must learn to balance fleet needs, knowing the right time to expand, while keeping large groups of your ships scattered in key positions to await reinforcements should the need arise.