TL;DR: Orwell’s ‘good bad’ poetry is ‘bad’ because it is superficial (lacking in aesthetic, intellectual, psychological or moral depth), but ‘good’ because it is skilfully written and enjoyable to read.
Orwell gave eight examples of ‘good bad’ poems, in addition to the works of Rudyard Kipling. I’ll give four lines from each, but follow the links for the full poems.
‘The Bridge of Sighs’ (1844) by Thomas Hood, about a young woman drowned in the Thames:
Take her up tenderly,
Lift her with care;
Fashion’d so slenderly,
Young, and so fair!
‘When all the world is young, lad’ from The Water Babies (1863) by Charles Kingsley, on the theme of tempus fugit:
When all the world is young, lad,
And all the trees are green;
And every goose a swan, lad,
And every lass a queen;
‘The Charge of the Light Brigade’ (1854) by Alfred, Lord Tennyson, about a disastrous maneouvre at the battle of Balaclava:
“Charge,” was the captain’s cry;
Their’s not to reason why,
Their’s not to make reply,
Their’s but to do and die,
‘Dickens in Camp’ by Bret Harte, which imagines a California pioneer reading aloud a novel by Charles Dickens:
And then, while round them shadows gathered faster,
And as the firelight fell,
He read aloud the book wherein the Master
Had writ of “Little Nell.”
‘The Burial of Sir John Moore after Corunna’ (1816) by Charles Wolfe, about the burial of General Moore after his death at A Coruña in 1809:
Slowly and sadly we laid him down,
From the field of his fame fresh and gory;
We carved not a line, and we raised not a stone,
But we left him alone with his glory.
‘Jenny Kissed Me’ (1838) by Leigh Hunt, also on the theme of tempus fugit:
Say I’m weary, say I’m sad,
Say that health and wealth have miss’d me,
Say I’m growing old, but add,
Jenny kiss’d me.
‘The Ballad of Keith of Ravelston’ by Sydney Dobell, about a wicked lord and a dead cowherd:
The murmur of the mourning ghost
That keeps the shadowy kine,
‘O Keith of Ravelston,
The sorrows of thy line!’
‘Casabianca’ (1826) by Felicia Hemans, about the death of Giocante de Casabianca at the battle of the Nile:
The boy stood on the burning deck
Whence all but he had fled;
The flame that lit the battle’s wreck
Shone round him o’er the dead
The great tradition
In order to appreciate the context in which Orwell was making his literary judgments, we have to think our way back into the mindset of the educated classes of England in the first half of the 20th century. The literary education of the upper classes was based on a ‘Great Tradition’ (in the words of F. R. Leavis) that ran from Homer through the classical Greek and Latin writers, through Chaucer, Shakespeare and Milton down to Eliot and James. The tradition is characterized by aesthetic complexity, intellectual depth, psychological observation, and moral seriousness; or at least it can be interpreted as respecting those goals.
To this stratum of society (to which Orwell belonged, however precariously: he was educated at Eton), ‘good’ literature consisted of the works of the great tradition and its followers, and ‘bad’ literature was everything else: comic and sentimental verse, folk songs, detective stories, ‘penny dreadfuls’, ‘three-decker’ melodramas, music hall, Western fiction, science fiction, and so on.
The late 20th century exploded the idea of the Western literary canon so successfully that this attitude seems quite blinkered to us now. Nonetheless, G. K. Chesterton apparently felt it necessary to write an essay pointing out that
many people do not realize that there is such a thing as a good detective story; it is to them like speaking of a good devil. […] There is, however, between a good detective story and a bad detective story as much, or, rather more, difference than there is between a good epic and a bad one.
(‘A defence of detective stories’, 1900.)
Orwell introduced his idea of the ‘good bad’ poem in the essay ‘Rudyard Kipling’ (1942), in which he reviewed the collection A Choice of Kipling’s Verse, edited by T. S. Eliot.
At his worst, and also his most vital, in poems like ‘Gunga Din’ or ‘Danny Deever’, Kipling is almost a shameful pleasure, like the taste for cheap sweets that some people secretly carry into middle life. But even with his best passages one has the same sense of being seduced by something spurious, and yet unquestionably seduced. Unless one is merely a snob and a liar it is impossible to say that no one who cares for poetry could get any pleasure out of such lines as:
For the wind is in the palm trees, and the temple bells they say,
‘Come you back, you British soldier, come you back to Mandalay!’
and yet those lines are not poetry in the same sense as ‘Felix Randal’ or ‘When icicles hang by the wall’ are poetry. One can, perhaps, place Kipling more satisfactorily […] if one describes him simply as a good bad poet.
At this point Orwell gave the eight examples, and then commented:
All of these reek of sentimentality, and yet—not these particular poems, perhaps, but poems of this kind, are capable of giving true pleasure to people who can see clearly what is wrong with them. One could fill a fair-sized anthology with good bad poems, if it were not for the significant fact that good bad poetry is usually too well known to be worth reprinting.
So what Orwell seems to have had in mind is that the ‘good bad poem’ panders to popular taste, but nonetheless it is a good example of its type: it is constructed with skill and enjoyable to read.
A quick note on ‘sentimentality’. The Oxford English Dictionary says
sentimental, adj. 1.a. […] Addicted to indulgence in superficial emotion; apt to be swayed by sentiment
It’s the superficiality that Orwell is complaining about, not the emotion. For example, consider the first of Orwell's examples, Thomas Hood's ‘The Bridge of Sighs’. This eloquently expresses the poet’s sadness, but doesn’t go any further than that. The young woman in the poem has drowned herself because she was homeless, probably due to a pregnancy, but the main matter of the poem is how beautiful her corpse looks and how her sins are forgiven now she is dead. If there is a moral, it is only “Alas! for the rarity / Of Christian charity”. This is liable to strike the modern reader as a superficial response: surely some thought ought to be given to the sexual double standard and the cruelty of the patriarchal society that shunned her?
Good bad books
Orwell elaborated his thoughts on ‘good bad’ literature in the essay ‘Good bad books’ (1945):
A type of book which we hardly seem to produce in these days, but which flowered with great richness in the late nineteenth and early twentieth centuries, is what Chesterton called the “good bad book”: that is, the kind of book that has no literary pretensions but which remains readable when more serious productions have perished. Obviously outstanding books in this line are Raffles and the Sherlock Holmes stories, which have kept their place when innumerable “problem novels”, “human documents” and “terrible indictments” of this or that have fallen into deserved oblivion. […]
The existence of good bad literature—the fact that one can be amused or excited or even moved by a book that one’s intellect simply refuses to take seriously—is a reminder that art is not the same thing as cerebration. I imagine that by any test that could be devised, Carlyle would be found to be a more intelligent man than Trollope. Yet Trollope has remained readable and Carlyle has not: with all his cleverness he had not even the wit to write in plain straightforward English.