tl;dr: This is good game. Cheap for what you get, lots of mods. Good optimization, much pretty. Music nice, gameplay nice, must play for space RTS fans.
Sins of a Solar Empire is a space RTS with no campaign, but endless replayability. Every game, the universe that the game is played in is randomized, or selected from a premade map (which offer specific challenges to make the game more interesting). There can be many stars in one universe, and each star can have very few or very many planets, asteroids, wormholes, etc.
The game offers a very nice blend of combat, research, and dimplomacy. But research really trumps everything, which leads into one of Sins' flaws... the difficulty curve
. This game will kick your ♥♥♥ if you are a newcomer to the RTS genre, and even if you are a veteran, you will find a good challenge. This game is not for the easily frustrated, because going against AI, or other players, can really pump up the blood pressure sometimes.
The game itself runs very well for my system. I'm running it on an AMD FX 6300 Processor, NvidiaGTX 660, with 8 GB of RAM, and it runs perfectly fine. It is very well optimized and looks beautiful. The backgrounds of space look phenomenal and the ships look pretty good too. Watching the space battles can be so nice to look at that you forget to make sure they are actually doing alright.
Anyway, This game is worth the $40, but I would also cash in for the DLC, because they are very good for the price. The modding potential for this game is amazing as well. If you ever get bored of the basic game, you can just browse the giant selection of quality mods on Moddb. If there is a popular movie/TV/game/book series taking place in space, there is a good possibility that there is a well made mod already created, or being crafted of it.
Thanks for reading, if you got this far, and I hope this review helps, although the fact that there are already 1,000's of positive reviews made for this game should be a clear indication of the quality of Sins of a Solar Empire: Rebellion.