Michael Rooker says folks are sleeping on Kevin Costner‘s new movie saga … telling us the film is a throwback to classic Hollywood and a departure from the “crap” TikTok generation.

We got Michael, who stars in Kevin’s new epic “Horizon: An American Saga — Chapter 1,” at LAX and our photog asked him about the film’s poor box office opening.

Michael thinks one of the reasons Kevin’s movie only grossed $11 million last weekend is because folks nowadays are used to short social media clips and 90-minute movies … not real, quality films with deep characters and rich storylines.

‘Horizon’ has a 3-hour runtime but Michael says people need to wake up and see the film because it’s “real cinema … not TikTok crap.”

Kevin invested a ton of money into the film himself, and Michael says this may just have to be a slow burn … with three more parts coming out, including part two fast approaching in August.

Seems like Kevin’s “Yellowstone” fans haven’t given him a ton of box office support yet … and Michael also has a message for anyone who is upset KC is leaving the show.