One of the big differences between traditional poetry and modern poetry is the use of form and structure. Traditional poetry is generally considered to adhere to specific forms, rhythms, and meters. Some examples of traditional poetry are sonnets, ballads, odes, and elegies. Traditional poems often rhyme (but not always) and they tend to have a specific and symmetrical structure. For example, Shakespeare's sonnets were written in iambic pentameter with a rhyme scheme of abab cdcd efef gg. Consider a more recent example of traditional poetry, Emily Dickinson's "Because I could not stop for Death" (1863). The poem consists of six stanzas, each with four lines. The first and third lines are written in iambic tetrameter and the second and third lines are in iambic trimeter.
Because I could not stop for Death--
He kindly stopped for me--
The Carriage held but just Ourselves--
Modern poetry is much more experimental in form. Therefore, modern poetry looks and reads quite differently from traditional poetry. Modernist and postmodernist poets (specifically in the 20th and 21st centuries) questioned the strict adherence of form and structure in poetic verse. So, there are some modern poems that seem to read more like prose than poetry. Consider a section of this poem called "Incident" (1969) by Imamu Amiri Baraka:
He came back and shot. He shot him. When he came
back, he shot, and he fell, stumbling, past the
shadow wood, down, shot, dying, dead, to full halt.
Although appearing less like a poem and more like a series of sentences sporadically broken by enjambment, this is still poetic. The blunt phrases and repetition emphasize the violence of the subject matter. The freedom to experiment with form made this effect possible.
Here is another example of modern, experimental poetry, E. E. Cummings' "[space being(don't forget to remember)Curved] (1931)." This poem experiments with form, structure, and language to create different juxtapositions of words that attempt to illustrate ideas about stream of consciousness, curved space-time, and relativity.
Space being(don't forget to remember)Curved
(and that reminds me who said o yes Frost
Something there is which isn't fond of walls)
an electromagnetic(now I've lost
the)Einstein expanded Newton's law preserved
conTinuum(but we read that beFore)