There's a lot of criticism of Bay but his films (mostly) sell tickets.
I think his signficant problem is his lack of interest or judgement in story or character.
His Benghazi movie, '13 Hours', got better reviews than most of his films. It seems he can tell a story, but needs help sticking to it. He's another director that needs good writers and a producer who wont let him just blow everything up.
His approach to 'Transfomers' though is very clear. Jerrod Carmichael was interviewed recently;
How was it working on a Michael Bay set?
It may have been the single biggest learning experience I have had in my career. A reason I wanted to do the film was to see what a production of that size was like and to see how comedy can translate internationally. You can say a quippy thing or something sarcastic but does that translate to China? Does it play well in India? It’s a skill.
On the first day, I said something that I thought was really funny and I even got the crew laughing but then Michael was like, "If you’re in China, what is that joke?" And I was like, "Oh, you’re right. That joke doesn’t work in China." So you learn to adjust. You have to think about comedy in a new way and that was a real challenge and I learned so much that hopefully I can apply it to my own work in some type of meaningful way.
That’s interesting that everyone on set is hyper-aware of how the movie will play internationally.
And no one more so than Michael. It was fun being around him because you learn to be unapologetic and to be specific and to consider your audience.
He doesn't think he's making art or curing cancer with these films. He's selling fun and spectacle to millions of people. That's it.