Basically, it's Space Invaders with Lumines aesthetics and a combo system. It just came out in Japan. According to Gamestop, both the DS and PSP versions (and, incidentally, Arkanoid DS) will be available here in the summer for $20 each. At that price, I suspect that the paddle included in Arkanoid DS and supported by the DS version of Space Invaders Extreme will not be making an appearance.
Here are two trailers:
If you have a PSP, you can also get a demo here.
I have just played a couple of games and am very impressed. I think the DS version is a little better. The boss shots in the PSP version travel at half the speed of normal shots - something not present in the DS version, as the boss fights (and the bonus rounds) use both screens. On the other hand, if you hate dual-screen displays, you'll probably prefer the PSP version.
The scoring system is fairly basic, but there's a combo system based upon shooting down a series of identical enemies, a column of enemies, or a row of enemies. If you rack up a chain of 4 twice in a row, a special ship zooms across the top of the screen. If you shoot that ship, you get taken to a bonus round where you're given a goal (typically shooting a certain number of a specific enemy) to accomplish. If you succeed, you enter a "fever mode" where everything is worth massive amounts of points and you have tons of firepower.
The presentation is astonishingly good. If any of you played Arkanoid DS, you'll know that Taito has been trying to copy the synaesthetics of Q Entertainment's games. They failed miserably with Space Invaders: Galaxy Beat and didn't quite succeed in Arkanoid DS, but Space Invaders Extreme is actually better than some of Q Entertainment's efforts. The graphics are trippy and reminiscent of Tempest 2000 or Space Giraffe and the music is fantastic. The sound effects are carefully integrated, always in time with the beat and changing based upon the song (and the section of the song playing).
Definitely give this game a try, even if you think Space Invaders is incredibly dated in this day and age.

