It can't get any worse, really
Transformers 2 was one of the worst movies I've ever seen and I couldn't remember a thing about Transformers 4 as soon as I took one step out of the theater. These movies honestly can't get any worse. I see that as a positive thing, since they can only get better. Also, part 5s in previously lousy franchises have a knack for being surprisingly good (Fast Five, Final Destination 5) so maybe this one will be another example of that.
But then again, Michael Bay directed. So it'll probably still suck.