Sam Witwicky, played by Shia LaBeouf, does not appear in "Transformers: Age of Extinction" due to a shift in the franchise's direction. The film introduces a new protagonist, Cade Yeager, portrayed by Mark Wahlberg, and focuses on a new storyline set five years after the events of the previous film. LaBeouf's decision to step away from the series, combined with the filmmakers' intent to refresh the narrative and introduce new characters, led to Sam's absence in this installment.

"Transformers: Age of Extinction" received mixed to negative reviews from critics, with a Rotten Tomatoes score of around 18%. Many criticized its lengthy runtime, convoluted plot, and character development. However, some audiences enjoyed the visual effects and action sequences typical of the franchise. While it may not resonate with critics, it found a fan base among viewers looking for explosive entertainment. Ultimately, whether it's "bad" depends on individual taste; fans of the series might appreciate it more than newcomers.

In "Transformers: Age of Extinction," the Autobot Ratchet dies. He is captured by the human organization KSI, which is hunting Transformers, and ultimately killed by Lockdown, a bounty hunter. Ratchet's death is significant as it highlights the ongoing conflict between humans and Transformers and sets a darker tone for the film, emphasizing the stakes for the remaining Autobots.

Mark Wahlberg left the "Transformers" franchise after "Transformers: Age of Extinction" primarily due to a desire to pursue new roles and projects. He expressed interest in exploring different genres and working with various directors. Additionally, the film received mixed reviews, which might have influenced his decision to step away from the franchise. Wahlberg's departure signifies a shift in the series, as the filmmakers aimed to introduce new characters and storylines in subsequent films.