Worth every cent
I wrote as a comment on Brad's review of the game that I was happy with the $15 I had spent on the game, and that it warranted at least a 4/5. That was about at about 5 hours of game time. I'm almost three times that deep into it now and I can fully reiterate that sentiment.
The game is absolutely gorgeous and I really find myself just stopping at staring at some of the environments (much to my detriment on some of the harder difficulties). The story is incredibly intriguing and dark as hell, which is all really just icing on the cake for a game like this, but I can definitely say that it is a huge part of my very positive review. Beating the story mode on challenging unlocks an alternative narration which doesn't change the actual dialog or any of the gameplay, but expands on the story and provides a 'true ending' which I would say, if the story interested you at all the first time through, is definitely worth playing to see. The story mode is very beatable for most gamers, as it comes with many continues and the overall play mechanic (getting hit reduces your remaining time rather than absolutely killing you, as well as jettisoning gun capsules, though you retain a minimum number of them on lower difficulties) is forgiving here. Ikaruga made me its bitch but I had no problem getting all the way though this multiple times. i'd rate its difficulty (on story mode ONLY) as comparable to Einhander for the PS2.
On higher difficulties, the mechanic is actually pretty punishing as making even a small mistake is hard to recover from. Arcade and score attack mode only allow you to play on hard or insane (the biggest difference I've found between these is that insane gives you even less time, and when anything explodes it releases a small bullet storm), which means that you will be replaying the hell out of stages to get them down pat. Arcade allows you to retain continuity (read: power ups) between stages, but score attack requires you to start each stage with a level 1 pea shooter which gives some stages serious, serious difficulty. The difficulty of these latter modes has turned some people off of the game, but the achievement system (if you're into that at all) gives it some direction and provides leveled benchmarks for you to gauge your improvement, and the overall experience is so enjoyable and addictive that even when I explode for the 40th time I still want to jump right back into it. I wouldn't call myself a serious fan of this genre, but I'm definitely a fan of this game. If you like a little challenge I would highly recommend it.