That is a common-ish feeling amongst people but it is one I've never understood.
To me the first is the absolute worst Bayformers flick because it is operating under the delusion that it is a real movie with real characters and real drama and thus it is held back from the insanity that will grip the rest of the series and reach its glorious apex with The Last Knight. Which is easily the best film in the series for its unrelenting disregard for everything: the previous movies, the story being told, the characters, the audience.
An excellent craftsman by the name of Michael Bay, backed by an army of talented people and with limitless funds, crafted a one-of-a-kind masterpiece in which you can feel both his love for the art form and his complete disdain for the property he is working on in equal measure in almost every scene.
I'll miss you, Cade Yeager, you All-American Texan, inventor, father, hero, everyman, inventor, Knight of the Round table, inventor, you.