TS Eliot's first work in his first book, and the title piece of that book, was 'Prufrock' - i.e. The Love Song of J Alfred Prufrock:
Full text of the poem: http://www.bartleby.com/198/1.html
It is a brilliant piece of work, extremely powerful, full of memorable lines (in that respect unlike almost any other example of modernist poetry) - it was also revolutionary in technique and attitude, and massively influential on later writers (and scholars).
Yet it is a horrible, fiendish production; that aims to induce - and successful succeeds in this task - a mood of world-weariness and despair; an attitude that it is not worth bothering with anything, because it will inevitably fail; a perspective that the good things of the world are illusion and the underlying solid reality is of ugliness, misery, lies, incoherence, ridiculous but self-aware vanity...
(The mainstream condition of modernity that Peter Sloterdijk terms 'enlightened false consciousness'.)
Prufrock is, in sum, the modern condition of alienation and hope-less-ness achieved perfectly in a single work at the first attempt and never surpassed.
Now I am not saying that TS Eliot was an evil genius when considered as a whole - of course he later became a very influential Christian of a traditionalist type; but the damage he did as a young man with Prufrock, and later The Waste Land, was never undone by anything he (or anybody else) subsequently achieved.
Prufrock fed an attitude of cynicism and - ultimately - hedonism and conformity (because all explicit cynics sell-out and become cogs of the system - at least all the many young cynics I have known have become middle managers or Establishment commissars).
Prufrock also led to the destruction of poetry - because it looked-like poetry, used various techniques of accepted poetry; but it was not poetry. It was 'poetry' minus the lyricism that made it poetry, 'poetry' without 'song'; 'poetry' with the essence of poetry extracted and replaced with subversion of lyricism.
Future generations followed suit, and the most 'respected' and influential 'poets' since Prufrock have not been poets.
(This was not an accident. Unlike - say - Yeats and Frost, Eliot was not a poet; and never wrote poetry (as poetry would have been understood in the previous hundreds of years). He was, of course, a prose-writer and versifier of genius - and that is why his verse is so effective; but he was not a poet, and could only pastiche real poetry. Nor did Eliot 'get' poetry, he could not detect its 'presence' or absence - which was unfortunate in the major literary critic of his age.)
(But then, neither did FR Leavis understand real poetry, nor CS Lewis, nor Empson, nor bloom... indeed real poetry is much too simple and lucid and popular to be a suitable theme for the powerful and influential critic.)
Prufrock, although easily appreciated by anyone, also triggered the cleavage between 'serious' writers aiming at an audience of critics, academics ad students on the one hand; and the spontaneously poetry-reading public on the other - and in a century this has grown ever wider.
Of course, all this would have happened anyway without Prufrock! - maybe half a decade later. So in that sense, the poem had zero influence. The culture had changed by a kind of mass embrace of the inversion of Good; Leftism was already pervasive among the intellectuals, the Great Apostasy from Christianity was too far advanced and celebrated; the sexual revolution already had the opinion-leaders in its grip; the mass media and the labilities of fashion were already a ruling addiction...
Hence Eliot's star, and Prufrock's fame' has faded and faded over the past decades. The brilliance of the decadent culture it inspired continued to glitter into the 1970s (Tom Stoppard - the best of recent playwrights - listed Prufrock as one of his major influences; Beckett was the other) - but has long since dimmed and extinguished.
Modern culture is Prufrock without the inspiration, without the sparkling wit, without the permanently memorable phrases.
We have lost or ditched the genius; and retained only the evil.