Several boss fights have been praised for their variety and strategy required to beat them. The series is notorious for its fourth wall breaking scenes. The storyline has been commented to maintain "rich characterization" while touching on some controversial themes. Hideo Kojima's ambitious script in "Metal Gear Solid 2" has been praised, some calling it the first example of a postmodern video game, while others have argued that it anticipated concepts such as post-truth politics, fake news, echo chambers and alternative facts. The series' storytelling in general has received praise for being among "the most fascinating science fiction stories in any medium". The series' cutscenes have often been praised for their graphics and the characters' stunt performances. Nevertheless, a common criticism has been the scenes' lengthiness, as well as some parts of the storyline. Raiden's unexpected introduction as the main protagonist in "Metal Gear Solid 2", due to his lack of appearances in the games' trailers and how he replaces fan-favorite character Solid Snake, has been deemed as one of the most controversial parts of the entire series. The series' audio has been acclaimed to the point of receiving awards for its use of sound and music.