A good concept, until you try to play for score.
Prior to playing Ikaruga, I had heard so much about it, from an X-Play segment to a Maddox article to whatever. So I found a copy of the GameCube version at
GameStop EB Games for $40 and decided to snag it up before it went Radiant Silvergun. (Which thankfully did not happen thanks to its XBLA release.)
I definitely enjoyed the polarity concept—it added a new layer of depth to the game the awesome orchestral soundtrack, and the meticulously placed enemies. However, the game's flaws started to set in when I tried to play for score. While the chaining system shows just how well Treasure placed enemies in the game, I absolutely loathed the rote memorization needed to master it. This is not like DoDonPachi's scoring system, which rewards paced, continuous destruction (and requries less memorization), or Space Invaders Extreme', which rewards creative and varied gameplay style and was not as overtly memorization-based as Ikaruga's. I try to do "screw it" runs consisting of me disregarding chaining altogether, but the constant me hearing "1 CHAIN" makes me remember how badly I suck at chaining and makes me not not care about chaining.
Everyone talks about how Ikaruga is the hardest game ever made. While it is difficult, saying that it's the hardest game ever is a bit of a stretch; I can one-credit this game on Normal up to Chapter 3, but Gradius III arcade version on Normal makes me choke starting at the 2nd or 3rd stage, Gradius IV says "fuck you you ain't getting past stage 3," and Mushihime-sama on Ultra is very hard on the first stage.
If you want a bipolar twist to your shmups, some fairly challenging gameplay, and can either stomach a chaining system that takes more memorization than Japanese kanji or can ignore it altogether, by all means give this game a go. It's only $10 on XBLA, and even if that's too expensive for you, you can try out the one-stage demo. If you like a more free-form scoring system, however, look towards another game, for your sanity's sake.