This is one of the best space invader games.
I've actually never thought it would be possible to make a Flash game of this quality, but here it is in front of my eyes. I believe this game deserves much more recognition than it already has - it is a solid game, which can keep you playing for more than a couple of minutes that most Flash games do. The music is very good, the graphics superb and the controls awesome. All this alpha blending might make some older computers to slow down a bit, but i've seen much worse graphics in Flash with less performance. No really, this could be a game you would buy for Wii or XBLA, but you have it right here for free.
An advice for new players: make sure the first update you get is speed and the second the weapon powerup. It will make your life easier.
I highly recommend this to anyone in need of a fast paced shooter.
Ah, btw. There is nothing "retro" with this one - its as new and fresh as it gets ;-)