The lack of save system hinders otherwise a great space shooting experience.
Story is extremely simple, which is probably an intentional choice. Earth has been invaded by hostile aliens and you as a lone pilot manage to steal an alien spacecraft. It's up to you to stop these aliens by turning their own weapon against them. Story is told through brief text boxes and you don't really care about the plot that much. What matters are the action and the overall presentation.
Graphics are brilliant with lots of bright colors, explosions and the frame rate stays solid all the time. Sound design works just as well and the musical score brings back memories from the early 90's disco music.
Gameplay is simple and fun. You fly forward away from the screen like in N64's Starfox instead of preferring a traditional top-down view like in Ikaruga. Between missions you may choose from 3 different paths and you can't play them all in your first play through. This adds a level of replay value into the overall package.
There's a support for 2 player multiplayer mode either locally or via Xbox Live. This kind of game is always at its best with a friend, but sometimes the amount of stuff on screen can get a little confusing with a 2 player game.
But then the problems start to gather. You can't shoot constantly by just keeping the A button pressed down: instead you need to tap it constantly. This is the first weird and bad design choice. The second is that there is no actual boss fights in the game.
The worse thing is the lack of save system. You only have a few continues at your disposal and when they are gone it's game over and you need to start all over again from the beginning. It would have been enough to be able to continue from the beginning of a specific mission like you can in Ikaruga or Assault Heroes for example.
Aces of the Galaxy has great features in it, but in the end I would recommend Ikaruga instead of this one.