There are other faces involved with guitar playing as well.

The Singer-Songwriter Face, invented and perfected by Bob Dylan, http://i.imgur.com/6mT4d.jpg is an expression in which one shuts their eyes tightly and angles their head backwards. While at first the eyes-shut portion of the face was done to indicate the depth of Dylan's emotion, the closed eyes are maintained these days so the poor bastard on stage doesn't have to look upon his single-digit coffee shop audience, thereby lessening the chance he will cry him/herself to sleep after going home that night.

The Sad Ballad Face, here as performed by Eric Clapton http://i.imgur.com/6dzWF.jpg has a strong resemblance to the Singer-Songwriter Face but instead of the head leaning backwards, it is dropped forwards. This is the traditional face for sad songs throughout any music genre. It lets the musician be alone with their feelings, letting their grief and sadness pour through their instrument.

The I'm Jumping Around Too Much To Actually Play My Instrument Face, perfected by the Dillinger Escape Plan http://i.imgur.com/wfXVG.jpg is endemic to guitarists who think the meat of their performance lies with jumping all over the stage, thrashing about, and being highly energetic. While their playing suffers as a result, you can't deny it makes for a entertaining show.

The Prog Face, here demonstrated by Focus during their live performance of Hocus Pocus http://www.youtube.com/watch?v=g4ouPGGLI6Q requires a video example because the Prog Face is as inexplicable and ever-changing as progressive music. A well-executed Prog Face is as unconventional, strident and generally unlikeable as the music.

The Modern Jazz Face is only a few shades away from the more common eyebrows-raised puzzled face people employ on a regular basis http://i.imgur.com/X8EZ9.jpg This is because the musician is constantly trying to evoke one very specific reaction to his music, summarized by the question "What the hell was that?" If the jazz guitarist is asking that of himself as he plays, he stands the best chance of success.