The Walking Dead returns to form in 100th episode as series eight begins

The first episode of The Walking Dead's eighth season has been praised for returning the show to its original form.

After critics savaged its seventh season, the world's highest-rated zombie show seems to have saved its plot by going into "all-out war".

To commemorate its 100th episode, entitled Mercy, the show's creators said they wanted to "thank the fans and give them something unique".

"It really gave us an opportunity to show the audience how far we've come," executive producer Greg Nicotero told the Hollywood Reporter.

"To pay tribute to the cast, every single cast member who has been on the show from the beginning and every crew member who has worked on the show, to go back to where it all started."

Without giving away any spoilers, many of the episode's scenes are an almost shot-for-shot reproduction of the very first episode, which saw main character Rick Grimes walking out of hospital to find the world taken over by zombies.

This season has been advertised as an "all-out war" between Grimes and villain Negan, with the hero having a bigger army at his disposal this time around.

In an interview with Entertainment Weekly, showrunner Scott Gimple said that, although the first episode posts more questions about the series finale, "we will get definitive answers".

Gimple also commented on one of the strangest soundtrack choices since the series started, Weird Al Yankovic's Another One Rides The Bus.

"One of the things I love about Weird Al is that there's no worry about cool, and cool is the worst thing ever," he said.

"Cool has infected my beloved comics and science fiction and fantasy and it breaks my heart, and I wanted to make sure we did not start out cool."

Gimple also promised fans "the most intense string of episodes we've had".

Critics seem mildly hopeful, with both Den Of Geek and Forbes calling the episode "interesting".

:: Season 8 of The Walking Dead starts on FOX on Monday at 9pm and will be available on NOW TV.