Love it or hate it, this is side scrolling action at its best.  I see that a lot of people complained that it borrowed from Metroid; I say kudos!  Metroid was also great and was in my opinion the best side scroller until SOTN.  You can read any number of reviews for the particulars, but I want to point out that this game is available for $9.99 to download from the PS3 store onto your PS3 or PSP.