I remember "Rock On" (somewhat), and that's the only Essex song I know. For me, there's nothing wrong with it, and to my taste, it isn't derivative enough to seem dated or uniquely bad enough to qualify as a guilty pleasure. There are lots of mainstream songs like this (different listeners will have different groupings--I think Leon Russell is solid but not stellar, but someone else will no doubt find his works stellar).

In a way these musicians we consider good-but-not-great are a kind of glue for pop music that their more brilliant but atypical counterparts need. If you took out all the non-memorable passages in a novel or movie, what you have left is like what the good-but-not-great musicians supply. Even within the works of a prolific and exemplary musician, there are albums / songs that are good-but-not-great. Yet these works contribute something that the best works by the same artist don't.