Microsoft sprung a surprise at Tokyo Game Show when they announced Space Invaders Extreme would get an Xbox Live Arcade port. Great, but what if you already have a copy of Space Invaders Extreme? According to the ESRB, Space Invaders Extreme for the Xbox 360 is Space Invaders Extreme plus Space Invaders.
"This is an arcade-style game in which players eliminate rows of alien space ships in order to clear game boards. The game includes the original version of Space Invaders, as well as new stages, bosses, and alien types."