Ikaruga is a shooter made by the genre's stalwort Treasure. Treasure have made many shooters on many platforms and have shown themselves to be innovative and most importantly capable of making great games. Ikaruga is one of their best games to date.
Ikaruga is a vertical shooter with simple but creative gameplay mechanics. You pliot Ikaruga, a ship capable of changing it's polarity between black and white. Enemies and enemy bullets are either black or white. This means that if an enemy is shooting black bullets at you, you can change your ship's polarity to black and the bullets will pass through your ship without causing damage. When you change polarity, your shots do too. Shooting an enemy with bullets of opposite colour will do twice the damage as shooting with the same. This one feature of the game is enough to elevate it above the rest of it's genre because it is executed sublimely and incorporated into the game intelligently. Different strategies can be employed depending on your goal. If you want to just survive, you can play it safe and use the polarity system in a defensive manner. If you're out for big points you can use it offensively and take out enemies quickly giving you better chance of chaining kills. Chaining kills is what gets you big points. Kill enemies of the same colour in groups of 3 and the score will shoot up.
Visually, Ikaruga one of the best shooters available. Even now, years after it's release it's still impressive. The backgrounds and ships are all rendered in well designed 3D. The nuclear style explosions when bosses are defeated is as expected of a shooter, wonderfully over the top. Music and sound effects are like everything else in this game, done well. Controls are responsive and proved to be up to the task when seriously tight maneuvering was required.
Like most shooters, Ikaruga requires a level of memorisation in order to progress. Stages can be impossible to clear unscathed unless you are familiar with the layout and where enemies will appear. Some may see this as a negative so I thought it prudent to point out. I didn't find it an issue personally as stages are quite short and making it further and further with each try was quite rewarding.