There’s a lot to like about All the World’s a Stage, the Keen Company’s new musical at Theatre Row, but the most likable item of all might be … the strings. Michael Starobin’s orchestrations comprise piano, cello, violin, banjo, and guitar, infusing Adam Gwon’s songs with warmth, color, and the sort of lush sound that new scores haven’t proffered for years. We’ve gotten so used to artificial-sounding synthesizers, ear-rattling drums, and over-miked accompaniment that Gwon’s and Starobin’s work sounds fresher and newer than anything going on at whatever jukebox musical is playing down the street. And it’s serving a story that bears telling, and is told well.