If you love an extremely simple, fast-paced game, pick this one up and also Geometry Wars: Galaxies while you're at it. If you're looking for an action game with some depth, go for Big Bang Mini instead.
Basically, this is the same old space invaders with a few "special" aliens (for example, some explode when shot), and some new temporary weapon power-ups you can earn by killing 4 or more of the same color aliens in a row. It's really just dodging bullets and shooting back at the slow-moving aliens, just like the arcade classic. If you're expecting anything more, like a new experience for example, you will be disappointed.