The movie, starring Mark Wahlberg and Anthony Hopkins, has just a 29 per cent approval rating on Metacritic.
It's even lower on Rotten Tomatoes at just 17 per cent.
The good news is that Bay is bowing out of the franchise after this one.
The bad news? Up to 10 sequels are reportedly being made.
Read a selection of reviews below:
"It is not so much lazy filmmaking as it is a very expensive middle finger to common sense and the basic concept of entertainment."
-Barry Hertz, The Globe and Mail (Toronto)
"The Last Knight is like a Red Bull-charged Bay yelling, 'I regret nothing!' as he jumps out of a plane backwards with no chute, detonating a megaton nuclear explosive while firing Uzis at his skydiving pals above him because hell, dude, that sounds like a wicked fond farewell." -Rodrigo Perez, The Playlist
"The latest outing suffers from arguably the most fatal flaw a movie about giant fighting robots can: it's brutally and relentlessly boring from start to finish."
-Dominick Suzanne-Mayer, Consequence of Sound
"When words fail in The Last Knight, the crunching and crashing and KLANKing of the special-effects scenes take up the slack. Punishingly overwrought in every aspect, Last Knight is a KLANK! KLANK! KLUNKER."
-Soren Andersen, The Seattle Times
"Watching an actor of Hopkins' caliber swear at his robo-butler and attempt to wring out laughs by uttering the word "dude" is painful - even for a Transformers movie."
-Johnny Oleksinski, New York Post
"Even with the low bar set by Michael Bay's previous Transformers movies, The Last Knight stands apart as an incoherent, disjointed work of visual anarchy, fanboy fantasy, mirthless mayhem and emo-starved characters."
-Dann Gire, Chicago Daily Herald
"Monster metal, mass destruction, Anthony Hopkins saying, 'dude'. This is your brain on Michael Bay-a cortex scramble so amped on pyro and noise and brawling cyborgs it can only process what's happening on screen in onomatopoeia: Clang! Pew-pew! Kablooey!"
-Leah Greenblatt, Entertainment Weekly
