Yes, Ikaruga is incredibly good. I've had the JAP version for a few months and have eventually completed it. Warning - you have no chance of completing it until you unlock Free Play mode (infinite lives, basically).
Its probably the most difficult game I have ever played and I am being deadly serious and honest saying that.
But, its a work of art as a game. There is so much tension built up that every second seems like life or death The game is so frantic that towards the end, there could be 60 or 70 enemies on-screen at once And thats just on easy. I haven't even touched the harder difficulty levels yet. All that happens with precisely NO slowdown during gameplay. At all. It is very impressive to watch, but takes on another dimension while playing.
I could say so much more but I might spoil something (wouldn't want to). I don't play many 2-D shooters but I enjoyed the hell out of this for the 9 hours + that I've played it.
Ikaruga is fabulous. Play it with a joystick for the proper arcade feel. The GC pad really isn't much cop.
I'm a big fan of 2d shooters and I would rate Ikaruga as one of the best. The colour/shield/charging system is novel and adds a real elememt of thought to the game.
Play it in co-op mode and try bouncing your companion into an incoming bullet of the wrong colour!