Final answer:
The first movement of Beethoven's Moonlight Sonata is best described as dreamy and ethereal, characterized by its tranquil, subdued emotions and a melody that floats above gentle arpeggios.
Step-by-step explanation:
The overall mood of the first movement of Beethoven's Moonlight Sonata can be described as dreamy and ethereal. This hauntingly beautiful movement, which is also known as the 'Adagio sostenuto', has a gentle and flowing character that invokes a sense of peaceful contemplation and otherworldly atmosphere. Unlike a stormy or passionate expression, this piece is characterized by its tranquil and subdued emotions, with a melody that seems to hover above the rippling arpeggios of the accompaniment.