My main issue with him is that he appears to have been tragically born without a personality. This can work, but mostly for weirdo octopus monsters like the Old Gods where we're not really supposed to understand or identify with them as they're supposed to be a weird horror.
The jailer, on the other hand, is a humanoid and part of a pantheon of other similar characters who all have personalities. It's also annoying we keep hearing about how he "convinced" characters like Sylvanas and Devos to join his cause, but he hasn't at any point done the same with us. He really hasn't explained anything. Everything I know about him has been from what other characters have told me, he hasn't shown us who he is at all. For all intensive porpoises the story would be more or less the same if we hadn't even seen him or knew of his existence yet.
When you first see him in the Maw and he crushes Anduin's bubble as you escape was about the ONLY time the jailer actually seemed like a character and less like a fixture. I figured he'd continue to have some more scenes like that but so far he hasn't done much of anything or been seen around.
I suppose now that Denarthrius is behind us we'll see more of the jailer's actual ..character.