Sword of the Stars is an unique take on the 4X genre, and therefore it's highly worth even with its share of problems.
The main goal of the game is making every turn, highly interesting and full of things to do: you can start building a fleet right at Turn 1, and keep up getting stronger with time. Of course this kind of setting makes for a strongly war-biased gameplay, that can scale from quick games of skirmishes in a little galaxy to epic struggles on hundreds and hundreds of stars.
The game is good and fresh in a lot of ways, but it falls short when compared to the depth of the masterworks: all you actually do is building ship, colonizing and researching, but you can actually manage very little on your colonies so you're just going to worry about upgrading your ships, making fleets and moving war.
Where the game truly excels is Tech Research: the tech tree is randomly generated at every game (so that you cannot count in advance on some tech) and showed in a very futuristic 3D fashion.
The six races feel and play very different from each other, starting with the way they move from one system to the other, so you're guaranteed to find lots of replay value.
While to this point it's all just "like it or not", the game also has some little problems that make gameplay a little bit frustrating. The star map is showed in 3D and, while this can be nice looking, it quickly gets confusing: if you're using the humans, all the "nodes" on which the human ships move will start showing on map and it can get a little bit hard to actually catch everything that is happening.
Also, there isn't a quick way to know if your building queues are empty or not, with the risk of wasting some turns.
Two words are needed for the tactical combat: it's managed on a 3D map but you can only move on a 2D plan. It actually plays nice, but the camera hardly makes it works, making it hard to follow the action. Also, there isn't a quick way to know the ship status in battle because the developers replaced the health bars with effective damage on the ship hull, which is cool but very hard to notice in the middle of a battle.
In the end, the game shows all the little design problems of a niche production; it plays great after all and can deliver lots of fun, but little problems with the UI and an unpolished RTS section show the limits of the production: I'd be glad to give back the 3D fight for a deeper 2D RTS sequence :)