Ikaruga is a vertically Scrolling shooter Video game made by Treasure Software that has been released on the Dreamcast and Gamecube as of October 2003.
The gameplay of the game consists of shooting enemies who are of one polarity - either black or white (though black is sometimes represented as red). The player's ship can be either polarity, with this polarity being switchable at will.
One unique feature of this game is the way in which only opposing bullets (i.e. a black bullet if the player's ship is white and vice versa) can kill the player. If the player is hit by bullet of the same colour, that bullet is absorbed and stored up - if enough energy is stored up, homing lasers can be released by the player, the number determined by the energy stored up to a maximum of 12.
The game also departs from other scrolling shooters in that most of its graphics are not bitmaps but full three-dimensional landscapes - this might be a constributing factor to the fact that there is no Playstation 2 version of Ikaruga, the rumour being that it wasn't possible to match the performance of the Dreamcast version (the Gamecube version has only recently been released).
In terms of difficulty Ikaruga it is considered to be slightly easier than Project-X, but not by much. A reason for this could be that the game design principles practised by game developers today (in terms of hardness, practice facilities etc.) did not exist at the time of Project-X, and if Ikaruga has been done then (disregarding that it would have been impossible at that time) or Project-X done now, they would be equal in difficulty.