'The Room' Star Understands Comparisons to Coppola's Polarizing 'Megalopolis'

Francis Ford Coppola either has another masterpiece, or a dud in his new "Megalopolis" movie -- and amid comparisons to "The Room," one of its OG stars is betting on Coppola.

Word outta Cannes is that FFC's self-financed passion project is such a mess that it compares to the 2003 cult classic film by Tommy Wiseau -- which has been labeled so-bad-it's-good.

Greg Sestero played the dude who was Tommy's best friend in the flick -- he was on the receiving end of Tommy's infamous "Oh, hi Mark" line -- and he told us if Francis' movie is being compared to their flick, he's most likely got magic on his hands.

Greg thinks "The Godfather" maestro clearly did something right if "Megalopolis" is getting trashed on the same scale as their movie. He can say that now because he firmly believes the lump of coal that was "The Room" became a bright shining diamond.

As Greg sees it, Francis had a vision, an F-U attitude, and the bucks to make his dream project a reality ... which reminds him of Tommy -- who put his all into "The Room."

His bomb became a fan fave, before a book and then a studio film retelling starring James Franco.

He offered this factoid to boost Coppola's spirits -- "The Room" has been screening around the globe for 20 years, and fans still love it.

BTW, "Apocalypse Now" also got mixed reviews when it first dropped ... and now, it's considered one of the greatest films ever.

Anyway ... if all this talk about "The Room" has you itching for round 2, we talked to Greg about that as well, and it doesn't sound like it's in the stars for now.

He thinks a Broadway musical could be awesome, or perhaps a TV series catching up with the bonkers characters. And yes, he still talks to Tommy, and says the last time they were together, they tossed around a football. Of course they did.