The poem "There Will Come Soft Rains," written by Sara Teasdale, uses indirect characterization instead of direct characterization. Upon first glance, the poem appears to have many characters -- frogs, swallows, robins, etc.; however, those living creatures are not the main character(s). If they were, then the poem might be considered to have more direct characterization. The main character of Teasdale's poem though is Mother Nature, and the outlook of Mother Nature is not a happy one. Sure the birds and frogs are happy and singing, but Nature itself is presented as completely uncaring toward mankind itself. The lines
"Not one would mind, neither bird nor tree
if mankind perished utterly;
And Spring herself, when she woke at dawn,
Would scarcely know that we were gone."
suggest that Nature does not care at all about the presence of humans. That's cold. At least loving or hating mankind would be an emotional response. That would show that Nature at least registers some kind of importance toward humans. A complete lack of realization that people are there or not means that Nature simply does not see any importance to people . . . at all. Teasedale doesn't say this directly, which is why it is indirect characterization.
As for structure, the poem is written in rhyming couplets. As for rhythm and meter, the poem is not consistent. It's close to iambic pentameter, but doesn't maintain it.