The tone of the first two verses is very pessimistic. Does the thrush and its song provide a more uplifting message however?
In the first verse Hardy writes 'Winter's dregs made desolate / The weakening eye of day'; the use of the words 'dregs' and ' weakening' provide the pessimistic tone suggesting things coming to an end or dying; the aliteration in the first line and the personification in the second only emphasise this pessimistic tone.
In the second verse nothing in the landscape provides any relief; the fact that a new century is coming serves only to remind Hardy of the previous one and make him mourn its passing, 'The land's sharp features seemed to be / The century's corpse outleant'. Once again the alliteration of 'century's corpse' emphasises the bleakness of the words. Furthermore, it is as if the poet is imposing his own bleak world view upon the landscape.
Hardy's melancholy thoughts are interrupted by the thrush's song 'Of joy illimited' and Hardy marvels at the sound and the fact that it is produced by a thing so 'frail, gaunt and small'. Crucially though, the poem ends on a pessimistic note as Hardy admits that he can see no reason for such 'blessed Hope' as the bird's song suggests.
Hardy can be charged with pessimism then; however, one should not ignore the other emotions such as wistfulness: if only he could feel the joy the bird does.