This is one of the best shmups I've played so far. Everything is great about it: stages, bosses, voice acting, soundtrack... and it's much better than the first game.
In the game, there are 7 stages (the final one is divided into two parts) and the main gameplay element is polarity switching which is also present in Ikaruga. Additionally, the game has difficulty scaling (the difficulty changes according to the player's skill) and chaining which grants bonus points and that's very useful for quickly getting extra lives.
The boss fights are very good because of the (mostly) epic music and the voice acting (most bosses say something according to your progress in the fight), which made the fights really cool at times.
The soundtrack is perfect because the songs are fitting for the given situation and they are top-notch.
My favorite part of the game would be the 7th stage because it's fun and it gets better towards the end.
I would recommend this game for those who are interested in shmups.