GSB is okay as a game. However, it is not a complete game in itself. The campaign is quite small and it does not go far enough with its technological 'skill tree' progression.
The gameplay is purely strategic and very hands-off. You build a fleet of ships, with the resources available, and you send them on their way. You have minimal control over how battles pan out, and there is no gameplay beyond the battles. Additionally, the interface is somewhat slow and unnecessary time consuming to navigate.
The most disappointing aspect of GSB is its blatant premium content model. After you have purchased the game, you will be required to purchase a number of nominally priced DLC packs to get the full game content. By buying this game, you are essentially only buying part of a game.
I give Gratuitous Space Battles 3/10 flaming spaceship hulls.