I never collected Transformers toys (except for the Beast Wars series in the 90's), and I watched only a handful of episodes of the cartoon series when I was a child, so I don't have as big an investment in the franchise and characters as a lot of people. As a relative newbie to Transformers in 2007, I really enjoyed the first Bay movie. And I'll be honest and say I enjoyed 2 and 3.
I do also recognise that the movies aren't neccessarily well-made. I know that these films largely consist of CGI action sequences connected by a simple and thin plotline. I know that they don't have ground-breaking scripts, cinematography, acting, or directing. I know that they aren't oscar worthy. I know that they are basic. I know that they don't require you to think too much and you can just sit back and absorb.
But I still enjoy them as entertaining action movies. I own them all on blu ray and have watched each of them more than once since owning them. You can enjoy a movie whilst recognising it's pitfalls and realising that there are far better films out there.