IGN's Craig Harris has posted some impressions of Space Invaders Extreme that are worth reading because they're impressions of Space Invaders Extreme. Oh, and they're quite positive: Craig says that Extreme "looks like it could be the best remake the franchise has ever seen." Wonder if he's played Akkanvader? Or if that's considered a sequel?
Thankfully, he explains the powerup system: shooting four Invaders of the same color imparts a powerup item, as we know, but the exact identity of each powerup was not. According to the article, "Red drops cluster bombs, green drops a wide spread gun, and blue unleashes a devastating laserbeam that can cut through the grouping in a single stream."
While we're examining Space Invaders, take a look at the lovely boxart found on the Gamestop listing for the game. Specifically, notice how it's different from the Japanese version in placement of Taito and Wi-Fi logos. There's also that ESRB rating, which doesn't show up on the ratings board's search page. In any case, this boxart and the listed publisher, Square Enix (who owns Taito) make us believe that Gamestop is not lying and the U.S. release of this game is for real.