I heard the first was good and the rest are shit. Is this true?

everything you like is shit

Yes.

A buddy of mine worked at Hasbro a few months ago, told me Bumblebee breaks Optimus's trance through the power of friendship, and that all the Decepticons act like gangsters. Transformers has always been a bit of a guilty pleasure, but Age of Extinction was trash and The Last Knight looks even worse.

The third one is objectively good too.

They're all varying degrees of bad unless there is robot action going on, which is surprisingly not often.