The game is a good short-lived time waster. What else did you expect for two or three bucks?
In Mass Effect: Galaxy, you play as Jacob, an Alliance soldier who is investigating some suspicious alien activity. You meet Miranda, a shady woman with lots of contacts and informants who help you on your quest. In the course of your investigations, you uncover an insidious plot against humans and save lots of lives. The story is not very long or deep, but it gives you some nice background on Jacob and Miranda, who Shepard recruits early in Mass Effect 2. For you to get anything out of this story, you have to play Mass Effect 2. If you haven't played that game and you don't intend to, then you probably won't get much out of Galaxy. The story is told in comic book panels, with you advancing conversations by selecting dialog options. There are renegade and paragon options in the dialog, but they don't appear to have any effect at all in the game.
The game alternates back and forth between dialog and shoot-em-up action. The action parts are very simple. You shoot anything that moves. To do this, you tilt your iPod to move Jacob around the screen and he shoots automatically. You tap the enemy that you want to shoot and Jacob takes care of the rest. You also have a grenade attack and a biotic attack that destroys enemies' shields. To unleash these attacks, you just tap their icons on the screen. The challenge level is appropriate and the simple gameplay works well. It is actually kind of fun because it doesn't try to do anything that the iPod or iPhone can't do. I had more fun playing this game than some other iPhone games that have tried to replicate a console experience by putting a virtual controller on the screen (such as Grand Theft Auto: Chinatown Wars).
If you are a big Mass Effect fan, then I recommend Mass Effect: Galaxy. It is fun for about an hour and then it ends. It is not a great and lasting experience, but it is worth the low price that you will pay for it now.