And one is of an old half-witted sheep,
And, Wordsworth, both are thine!
I've filleted J. K. Stephen's sonnet there, but those are officially the best bits - the rest is filler. And of course it's perfectly true - some Wordsworth is wonderful, but he can also be banal.
Of course, most poets write better at some times than others. It's the norm for novelists, artists and composers, too, maybe in fact for pretty much any human activity. But the badness of early Wordsworth, at least, is interesting. In that early work, bad Wordsworth and good Wordsworth aren't really very different from each other: each continually teeters on the other's brink. When your shtick is using ordinary language and everyday situations, banality is never going to be more than a redundant syllable away. (W. D. Snodgrass's De/Compositions: 101 Good Poems Gone Wrong illustrates this beautifully.) A change of light can prove your fairy feast a pile of stinking leaves, or blow beauty into a drift of dirt.
It's different from the badness of late Wordsworth, such as his sonnet sequence in praise of capital punishment:
IS 'Death', when evil against good has fought
With such fell mastery that a man may dare
By deeds the blackest purpose to lay bare?
Is Death, for one to that condition brought,
For him, or any one, the thing that ought
To be 'most' dreaded? Lawgivers, beware,
Lest, capital pains remitting till ye spare
The murderer, ye, by sanction to that thought
Seemingly given, debase the general mind;
Tempt the vague will tried standards to disown,
Nor only palpable restraints unbind,
But upon Honour's head disturb the crown,
Whose absolute rule permits not to withstand
In the weak love of life his least command.
Why this is not as good as the Lucy poems is not something I propose to discuss here; I leave that to the sagacity of the reader.
Anyway, this all prompts me to ask: what other writers exhibit the quality of keeping greatness and banality not at opposite ends of a spectrum, but as each other's shadows? I'm sure Wordsworth isn't alone.