Alien Apocalypse 2

This game is one of the best freeware space shooters you will find.
The main attraction of the game lies in its playability. A wide variety of levels, power ups and shields ensure that you will play it for a long time.
Special care has been given to the creation of interesting end-of-level bosses. Expect many lasting and challenging battles with level baddies that use a great variety of attacks to encounter you. A boss fight won't just indicate the ending of a level any more, it's gonna be the level's climax!