It contains some blues-rock (including a lenthy jam that *might* bore you to tears; I dig it a lot though) but also mellow acoustic songs, hard-rock and strange instrumentals in the vein of "Albatross". It's a bit of a mess but it's a really cool record even if it would have been better if they included their non-album singles from the same era.

BTW, an obscure, mellow Fleetwood Mac song I *LOVE*: Dragonfly http://www.youtube.com/watch?v=z0qvH_UisaM It never appeared on any of their regular albums to my knowledge and I only heard it on some budget german singles comp.