This game is 2D oldschool sidescrolling shooter. It brings some new play mechanics that are fresh but not revolutionary. Only if you like shooting games or challenging games should you buy this game, otherwise rent to see if it suits your tastes. This game was definitely targetted at the very hardcore 2D enthusiasts out there.
This game is a game about skill plain and simple, the game plays like Gradius or other vertical arcade shooters. You can choose you play verticle or horizaontal in Ikaruga so it my comments about gradius translate just fine for the people that only played sidescrolling ones.
Ikaruga is really about chaining and getting a highscore it's not really about you being a lone guy with a spaceship out to save the galaxy. In fact there is a complete absence of story text in the game that is in the Japanese version.
The bossess and enemy designs have nothing to do with an attempt at realism. The graphics are done well for the type of game it is and considering you dont see them for very long because your destroying them so fast they are definitely acceptable.
The thing I love about Japanese game developers is that 1) They know how to make games but the bad thin is that their backstories are often quirky/weird and ridiculous and probably alienate anyone who is not Asian or Japanese.
I think gradius was heading in the right direction by adding FMV's to the PS2's conversion of Gradius III and IV but Treasure eschews FMV and goes straight for gameplay and 'in game' cinemas (the short stints in between level sections where your ship performs a boost and a turn). The levels themselves are really the 'dramatic cinematic vistas' but all of the levels are very well done and intense (although short). This is a great pickup game. You can finish the game in 15-20 minutes once you get past the difficulty.
This game is SHORT and hard but you can tell the way the enemies path into the screen and the obstacle are layed out were designed very well with a LOT of care. You can tell ALL of the design work went into the puzzles and enemy placements for chains in the levels. This is where you'll truly appreciate the developers behind Ikaruga. To think and plan enemy patterns in such a way to make them chainable in combo's must have taken some serious thought and level design skills. If in doubt do a google search for "ikaruga replays" or "ikaruga avi" or mpegs and see what the best players can do. It will shock and appall you it will also give you some sick sense of envy of their talents because you know first hand how hard Ikaruga is!
Anyways Ikaruga is a great game but probably a rental for most. My recommendation: Only if you are hardcore about shooters or into the chaining aspect of Ikaruga and getting a highscore should you buy this game.