This is exactly what I call a prog song. A gentle ballad, featuring a well found melody, with a good deal of vocal harmonies too. Then, a series of isnstrumental parts, ranging from the most structured ones to apparent improvisations. In their first album, Gentle Giant were already fit for the great prog game, as this song proves too well. Guitar strong riffs, heavy rock vocals, drum solos, fully melodic themes, classical music quotations, free jazz passages go side by side in a single track.
Gentle Giant's first album was a real prog Landmark.
Unpredictable is the word to describe such an ever changing song... nine minutes of musical adventures! If the Giant's name is so popular today among all prog fans, whatever their favourite sub-genres are, is for this fantasy-driven kind of compositions. Many bands tried to re-create a song like "Nothing at All", some actually succeeded, but no one did it better than the Giant, believe me.