If you checked out the last free games post, you probably discovered that many flash games are a little on the dull side. But this week at Kotaku I found a link to a great flash version of the first boss fight from Ikaruga. As a game it's short, but also very impressive for a free flash game. It's all there: lots of bullets and polarity flipping.
I don't think the controls are in English. It should be easy to figure out if you've played Ikaruga before. Z: shoot. X: switch ship polarity. C: Energy release special attack. The arrow keys move your ship. Polarity flipping lets you absorb bullets that are the same color as your ship and charge your energy attack, but being the opposite color of your enemy increases your firepower against it. You may want to reduce the screen quality, even to its lowest setting, to prevent some slow-down and play the game at something like the real speed.
I'd love to see more flash versions of levels from Ikaruga. That game is one of the best Gamecube games and a contender for best space shooter of all time. It is certainly one of the most beautiful games ever. Long live shmups!