Galaga [Xbox Live]

The sequel to Galaxian, Galaga is a timeless classic, showing up regularly on fans' and magazines' lists of greatest games ever. As with most slide-and-shoot games, players control an upward-firing ship that moves horizontally along the bottom of the screen. Bug-like alien invaders fly in looping, twirling maneuvers around the screen, settling temporarily into formations at the top of the playfield, only to swoop down again. What sets Galaga apart from most blast-a-thons, in addition to its perfectly balanced shooting action, is the strategic maneuver of letting your ship get captured, then rescuing it for double firepower. Also nifty are the challenge stages, which let players blast away unmolested for extra points.

source: http://www.allgame.com/