Limericks are (meant to be) funny, even naughty, probably from their origins in pubs. They often contain hyperbole, onomatopoeia, idioms, puns, and other figurative devices. The last line of a good modern limerick contains the punch line, although Edward Lear’s limericks seldom had one. But it is the rhythm and the strong rhyme pattern that set limericks apart from "real" poetry. When a limerick is bad, it is painfully so, since there is no redeeming virture or noble sentiment to rescue it.
There was an Old Person of Buda,
Whose conduct grew ruder and ruder;
Till at last, with a hammer,
They silenced his clamour,
By smashing that Person of Buda.
There was a young hunter named Shepherd
Who was eaten for lunch by a leopard.
Said the leopard, "Egad!
You'd be tastier, lad,
If you had been salted and peppered!"
An epicure dining at Crewe
Found a very large bug in his stew.
Said the waiter, "Don't shout
And wave it about,
Or the rest will be wanting one too."
There was a young woman named Bright
Whose speed was much faster than light.
She set out one day
In a relative way,
And returned on the previous night.