From George Downes's Letters from Mecklenburg and Holstein; comprising an account of the free cities Hamburg and Lübeck written in the summer of 1820 (London 1822).
This account, all too brief, is interesting because it comes so shortly after the establishment of the controversial Temple (1818) and only just before the appointment of Chacham Isaac Bernays, a modern (small m) Orthodox rabbi (1821) as Chief Rabbi of Hamburg.
In his account, Downes describes the hats worn by "the rabbies" (more likely, the rabbi and community notables) and which is probably the schabbes deckel, as I posted about here. He describes the bowing gesticulations of the cantor, presumably at the end of the Amidah.
He also contrasts the lighting in the old and new synagogue. In the old one, ten yellow tapers stood on each side of the pulpit. In the Temple, the lighting consisted of candlesticks painted blue and gilt. He also describes part of the prayer service, which consisted of German hymns, with occasional Hebrew and Aramaic phrases.