It's been a while since I finished any game on any platform, but this game got me to finish it, which speaks very highly of it. The game's premise is that you're a space station commander that's supposed to mine asteroids. You built platforms and power connectors and miners, and of course, laser turrets, missile turrets, rail guns, and other support units. The structure is extremely free form --- you link the objects however you like constrained by the distance between structures and available connections.
Of course, while you're doing this, the enemy is sending you various ships to attack you, starting from light fighters easily dispatched by laser guns, and ending up with dreadnaughts, fighter-carriers, and other vessels which require heavier weaponry. The game seemed really tough at the beginning but after a while I realized that I had to visit the shop in order to upgrade my station's capabilities, buy additional weapons, and other upgrades. You get these credits by playing in the "open" modes (non-scenario modes), and by finishing scenarios in the main campaign. Or you could spend real money and skip the tedium. To the game's credit, it wasn't very much tedium and the open modes are good for exploring tactical or strategic changes to your approach. The reason the game has a comparatively low score on Amazon is that many reviewers seem to think the "tedium" of playing the open mode is excessive. I didn't think it was. In particular, it took several battles before I realized that one of the major constraints was power --- several laser turrets going at once can severely deplete the power on the station, which meant it didn't matter how many resources you were mining as you could not have all your guns operating at once. I thought this was a very clever constrained and the game had many ways for you to manage those constraints. It's a smart combination of a resource-gathering RTS with the tower defense genre.
In any case, as the campaign progresses, your missions get harder and also more interesting. For instance, the last 5 scenarios has you defending a crippled ship in addition to the space station. Many scenarios are "survival" scenarios, where you basically have to last a certain amount of time --- defeat is almost certain, so surviving that time was all that mattered.
What's interesting is that the Amazon Appstore sells this game for $1.25, while the Google Play store charges $1.98. I have no idea why there's this gap. In any case, I consider the price at either store to be a bargain. This game was lots of fun and great on a 7" tablet (either the Kindle Fire, which I was using, or the Nexus 7). I would definitely look forward to a sequel, if any was forthcoming.