Ikaruga is one of the best Live Arcade games.
Story of Ikaruga is pretty interesting, but the way that it's told is not. I had to look in Wikipedia in order to know anything about why the things on screen happen as they do. Several years ago in the small island nation of Horai, a man named Tenro discovered Power of the Gods. Soon after this Tenro and his followers began conquering nations one after another. Meanwhile, a freedom federation called Tenkaku emerged to challenge Horai. A young man named Shinra was shot down near a remote village called Ikaruga and the inhabitants entrusted him with a fighter plane that they had built themselves. It's the first fighter built that integrates both energy polarities and is capable of successfully switching between the two. As you might notice there are some similarities in the plot to the classic Star Wars movies.
Graphics are colorful and detailed giving you a real eye candy to look at. There's always something flying and exploding on screen, but still the frame rate stays solid all the time. Music is also grand and big giving a feel of a large space opera to the whole game. Sound effects are also great: when you are firing a fighter jet's laser cannon it really feels like it.
Gameplay is very simple top-down 2D shooter: just move around with the left analog stick and keep the A button pressed down to shoot a constant flow of laser. The catch here is to rapidly change between light and dark polarities: if you are on the light side the light beams will not hurt you and when in dark side vice versa. It sounds simple, but to master it in the heat of battle is a whole another thing.
Ikaruga has only 5 chapters in it, but still it's an insanely hard game. On the default difficulty setting there are no continues to choose from, but luckily you can change the difficulty setting as you see fit.
Game is at its best when playing co-op with a friend either locally or through Xbox Live. Both ways are working perfectly and since the game is so difficult I highly recommend that you bring a friend with you when fighting against Tenro and his followers.
Ikaruga is worth every Microsoft point you need to spend in it.