What can you say about the form of John Dryden's poem "Absalom and Achitophel"?

The poem "Absalom and Achitophel" uses an aa, bb, cc, etc. rhyme scheme and is set in iambic pentameter.

Every two lines rhyme in this poem; for the most part, the rhymes are perfect, as in "begin/sin" or "bore/before," although the poet also uses near rhyme as in "none/Absalom."

The iambic meter means that an unaccented syllable is followed by an accented syllable. Each pair of unaccented/accented is identified as an iamb. Here is how that works out in the first line, which establishes the meter:

in PI- ous TIMES, ere PRIEST- craft DID be- GIN

There are five iambs in each line, which is the "pentameter" of iambic pentameter.

It is fitting for a very long poem to be in iambic pentameter. After all, Shakespeare wrote parts of his plays in iambic pentameter (but did not always use rhyme). Much later in poetic history, Robert Frost used a loose form of iambic pentameter in his long poem "Birches."