The main character in The Mandalorian has yet to take off his helmet - it's possible that he never will - and viewers have been wondering what he looks like under there. Star Wars has a long history of hiding characters' faces with helmets, hoods, and other materials, going back to the original trilogy. Sometimes the look becomes a core part of a character's design, in the case of Darth Vader, or sometimes it's a simple way to disguise them, such as when Leia’s face was hidden under the Boushh helmet at the beginning of Return of the Jedi.
In the case of The Mandalorian, there's a good reason why the Mandalorian never removes his helmet. This is all part of the Mandalorian culture; they don't remove their helmets at all, which is something that was explicitly mentioned in The Mandalorian episode 3. In that episode, the Armorer asked the Mandalorian if he ever removed his helmet, and he answered no. But that doesn't mean he may never remove his helmet in the future. After all, this is a TV show and the main actor should, at some point, be seen by audiences.
Despite the helmet, though, some inferences can be made to help paint a picture of what the Mandalorian may look like. The life of a bounty hunter isn’t easy. The job comes with many perilous tasks and often times involves a fight. Because of this, one can guess that the Mandalorian may have a scar or two underneath his helmet, possibly even from his childhood when his home was attacked by droids. But considering that viewers know Pedro Pascal is playing the Mandalorian, the character will surely look like him, unless he's been covered in prosthetics.
Furthermore, The Mandalorian's flashbacks reveal what he looked like as a kid. In one of the flashbacks, avoiding the devastation during the droid attack on the Mandalorian's home, his father puts him into an underground shelter before shutting the door. These flashbacks could potentially be of the Siege of Mandalore which took place in 19 BBY. If the young Mandalorian was around the age of six or seven in these flashbacks, then this means that he's around 35 years old now, since The Mandalorian series is set around 9ABY.
The Mandalorian's face may never be revealed, but as new episodes of The Mandalorian release we learn more about the personality of the man under the helmet. The mysteriousness may not be what some fans wanted. However, leaving the appearance up to the viewers' imagination could be the best thing for the character and The Mandalorian series. In doing so, it allows the Mandalorian character to maintain his mysterious cowboy-like personality while letting the viewer construct their own imagined version of who’s under the helmet.