I know that wallpaper is one of those contentious things, what with the work that is required to get rid of it, but what if it looked like this?
and you could design your own pattern? and it was temporary (just attached with some bits of double stick tape) and it meant that you could have painted walls even in a rental where painting was a no no? AND it was made of 100% post consumer recycled paper? I say 'yay' to all those things.
These Paper Wall Tiles by Mio are available in natural or white and come in four patterns, including one "Designed to diffuse sound and reduce acoustic glare". Each tile is 12" x 12", they start at $32 for a pack of 12 tiles.