The mood of Mrs Dalloway is contemplative, as the detail-oriented narration invites readers to really reflect on the ordinary—but nonetheless fascinating and beautiful—aspects of everyday life. To that end, there's a sense of wonder and appreciation at play in the narrative, as the novel's interest in drifting in and out of the characters' lives creates a feeling of strange cohesion, even if everyone is experiencing different things—and this cohesion, in turn, ultimately gives readers the feeling that the novel is helping them tap into something profound and beautiful about humanity and the world itself.
At the same time, the novel certainly delves into private moments of despair (like the kind of lonely despair Septimus experiences during his war-related hallucinations), but the mood is still quite exuberant in the majority of the book. This passage at the very beginning of the novel is a good illustration of the joyful, appreciative tone that often comes into play, especially in sections in which Clarissa Dalloway takes in her surroundings and thinks about life:
In people's eyes, in the swing, tramp, and trudge; in the bellow and the uproar; the carriages, motor cars, omnibuses, vans, sandwich men shuffling and swinging; brass bands; barrel organs; in the triumph and the jingle and the strange high singing of some aeroplane overhead was what she loved; life; London; this moment of June.
The long list of observations about the bustling environment surrounding Clarissa creates an exuberant tone, making it clear just how euphoric Clarissa feels in this moment, as she revels in the excitement of the city. What's more, this string of thoughts leads her to think about how she loves life in general. And though the novel is certainly full of melancholy and sorrow in other sections, this exultant tone at the very beginning of the book establishes that it is, in many ways, a celebration of life.