As for the exposed mouth, that's not as unrealistic as you might think. There's a reason why often soldiers faces aren't covered in armor: The part of the human body that people whose jobs may require shooting at another person (Military, Law Enforcement, et cetera.) teach you to aim for center mass, because, in spite of what most first-person shooters will demonstrate, it's actually pretty hard to score a headshot, especially on a moving target. Furthermore, it would be pretty hard to design armor that you can breathe through. Soldiers generally only wear gas masks when they are needed, otherwise it would be pretty hard to do things like hydrating and so on. In Batman's case, I doubt that he would run into an NBC situation often enough as a crime fighter to warrant having one over his face at all times.