We might describe the tone of Eliot's well-known poem as "bitterly impassive."
Opening the poem with a faux-romantic invitation to explore the contemporary imagination, Eliot compares this little imaginative space to a patient "etherised upon a table."
The modern spirit is, then, conducting an investigation of itself - playing doctor and playing patient. The poet represents the subject and the speaker. Each are affected by the disillusionment of the modern day and each are powerless to escape that disaffectation and so must develop a sense of detachment. We might say that the effort to cultivate this detachment is, effectively, what the poem is about.
The tone then is ironic, supercilious, bitter, dreamy and romantic all at once.
The romance comes in the fact that the poem seems to yearn for a time before modernity (because, as the poem outlines, modernity is simply "not enough" to satisfy the spirit). The poem details the many tedious and false aspects of life in (high) society that characterize the modern era (in the 1910s).
Suggesting that death will come after a life made up of nothing more than these tediums, the poem's narration takes on an ironic distance from the tea parties, the dinner conversations, the decisions about how to wear one's hair, etc. Yet, despite the ironic distance and the attempted emotional distance, the poet cannot separate himself from that world and, unfortunately, cannot see much redeeming value in that intractable connection.
"Although he understands the mediocrity of his surroundings and of the society he frequents, he cannot rise above them" (eNotes).
In such a spiritual crisis (wherein life's meaning is always and only of the pettiest variety), the poet is bitter - at his powerlessness to truly escape, at the double irony of his ironic detachment (he has to look at himself ironically too, knowing that his emotional distance actually implicates him in the emptiness of his social world).