Regarding Issa, what I said in The Haiku Handbook still expresses my deepest feelings about him:
It is easy to sentimentalize, and thereby trivialize, the life and poetry of Issa. Japanese, as well as Western translators, have often been guilty of doing so. But Issa's verses are usually clear of such sentimentality, the few popularly remembered exceptions notwithstanding. We must not mistake the sympathy, the empathy Issa feels for those who seem to be "underdogs" as pity. People who have not experienced such hardship feel pity for those who have. Issa himself lived through many hardships; when he encourages even grasshoppers and frogs in the face of their adversities, he encourages himself.
Issa is also capable of lovely serenity and aesthetic sensibility, and of seeing the humor that constantly plays about human concerns:
the coolness . . .
the half-moon shifts
morning glories he sells,
* * *
leads into the mistó
low tide beach