The title is accurate; this is a collection of preliminary songs for Over the Garden Wall. In its short run time, it has peaceful instrumentals, tinted with a hint of melancholy, a few upbeat and humorous songs, and one that's genuinely pretty menacing.
It's fun to listen to this album and picture how it expands the world of Over the Garden Wall. Imagine the uses of these songs, either in the episodes that we have or those never made. Great album.