This mutual series of reprehensions is currently the only real deviation from the topic. One could have just left my first casual remark as it was-so don't try to pass the buck to me. And about the age: when I was 14, I knew better than to trivialise "domesticated" big cats.
Sorry @Pygathrix, no QED for You today. Better luck next time...
As I'm already here: I don't know whether it was already mentioned here, but another feature that can create "boring" animals for most visitors crossed my mind: the (animals') way of life. Even within nocturnal houses, You have species that don't display any behaviour attractive for most visitors, which means: they sleep or hide most of the time. As most people's attendence spane is rather short, a rather quiet and introverted lifestyle can soon label the species "boring".
Size is another matter, especially in already mentioned nocturnal houses; how often have I watched people quickly walk past Microchiroptera, little rodents or Insectivora exhibits because they can't see them at once. (Maybe one should try to teach people to be more patient, but that's a very unthankful task).
Thirdly, an attribute I think is one of the most important ones when it comes to judge about the "show effect" of the animal: how familiar is it to You?
This partly involves the standard collection species (neglected by many zoo fans), but also animals that look similar or are the same species people encounter quite often at home. A dingo is therefore "just another dog", a Crete Spiny Mouse is "just a mouse", a Red-legged Sun Squirrel is "just a squirrel" and a Travancore Tortoise "just looks like the tortoise we have at home". The less familiar the animal is, the more likely it might not be "boring" for the public-unless they easily get used to it...