If you wanna play the old Space Invaders, Google it. If you want an updated version, get Space Invaders Extreme (DS).
This leaves you wondering why you would pay $20 for Space Invaders while being able to play it free. Well according to the back of Space Invaders Revolution's box, you can play the classic game along with the "New-Age Version" that offers "More than 60 levels and 20 locations..." leading the buyer to beleive that they can play their favorite Atari game on updated levels with awesome design. But that's not the case here.
Space Invaders Revolution has the same exact stage on every level with a different background image and different sized aliens. Yes, the graphics are updated but only to the extent of a GameBoy Advance game, not making the use of the DS's new and improved graphics except for the opening cut-scene.
The music is fine, and fits the theme of where you are supposed to be in the game. And the sound effects are that of your basic arcade shooter.
The bottom line is that this is waste of your money. You can play the original Space Invaders for free easily. But if you are truly looking for a Space Invaders update that gives you the Space Invaders feel along with an update in graphics, sound, and gameplay then search GameSpot for Space Invaders Extreme for the DS.
If after reading this and researching the game and you still want the game, then get it off e-bay for a couple bucks, because that's all its worth.