Quite simply, amazing.
Few games pull off all areas of production so flawlessly as Supergiant's masterpiece, Bastion. From the art-design to the soundtrack to the gameplay everything is incredibly well executed and leaves you craving more even after the credits roll. Even though the story can be completed in around 6 hours, the option of a New Game+ and score attack mode will have you coming back. Aside from that, the incredible atmosphere and innovative storytelling will leave you wondering why other studios with much more money haven't been able to produce something as affecting as this game.
Long story short, BUY THIS GAME.