As mentioned, the vacillation of Hardy exists, so much so that he has been called, "The Good Grey Poet." This is what makes him such a vital poet and one to whom so many readers can relate. Donald Davie suggests in his work, Thomas Hardy and British Poetry,
Each reader finds in the poems what he brings to them; what he finds there is his own pattern of preoccupations and preferences. If this is true of every poet to some degree, of Hardy it is exceptionally true.
Indeed, Hardy, like the musician, plays to the heart of the reader.
One of the things I appreciate about Hardy's poetry is the way that often it oscillates between hope and despair and certainty and uncertainty. There is often an ambivalence in his work that on the one hand contradicts the overall depressive tone that he creates, and on the other hand supports it. Poems like 'The Darkling Thrush,' for instance seem to offer hope with one hand whilst snatching it away with the other, making us intensely unsure about what Hardy is trying to say.
To read Thomas Hardy's poetry is to appreciate bitter irony and cynicism. In "The Man He Killed," for instance, Hardy's speaker calls war "quaint and curious." This vast understatement reminds us of the dreadful cost of war in which young men slaughter each other for no other reason than they "were out of work," and there was nothing better for them to do than to join the military. Irony plays a part in "Are You Digging on my Grave," a poem that shows even man's best friend, a dog, does not grieve his mistress when she is gone. Life goes on. "In Convergence of the Twain," man's foolish boast that he is superior to nature is disproved by the Titanic in ruins at the bottom of the ocean and the fish wondering "What is all this vainglorious doing down here?" The foolish pride of man, the folly of war, the transcience of life are are treated with an ironic and bitter tone, making his poems haunting and memorable.
Thomas Hardy was a realist, someone most would call depressingly realistic. He wrote in this realistic style following the Victorian period, making his themes seem even more dismal and even dark. His poetry generally reflects his own experiences, and he is often the unnamed speaker of his poems. There is a hunger, a longing, a desperation, I find, in much of Hardy's poetry; and it seems to me that's what connects his work to even modern readers. I would not call his work particularly artful or imaginative or ingenious, though others may find it so. Instead, I find him relatable and accessible in a way many poets are not. You ask how we are to read Hardy's poetry, and my simple answer is to read it with an open heart and an understanding that this is a man who wrote about what he felt and saw and remembered.