All's Well That Ends Well is 55% verse (poetry) and 45% prose (how ordinary folks talk every day). (Source.) There are two main kinds of verse in the play: (a) blank verse, also known as unrhymed iambic pentameter and (b) rhyming couplets. Let's discuss.
Blank Verse (a.k.a. Unrhymed Iambic Pentameter)
Most of the verse in this play is unrhymed iambic pentameter (a.k.a.
blank verse). It sounds a little scary, but it's actually one of the most common and natural sounding verse styles in Western literature. Let's start by breaking down the phrase iambic pentameter: an iamb is an unaccented syllable followed by an accented one, penta means five, and meter refers to a regular rhythmic pattern. So iambic pentameter is a kind of rhythmic pattern that consist of five iambs per line. It's the most common rhythm in English poetry and sounds like five heartbeats:
ba-DUM, ba-DUM, ba-DUM, ba-DUM, ba-DUM.
Let's try it out on this line, where Helen gushes about Bertram:
his ARCHéd BROWS, his HAWKing EYE, his CURLS
Nice. Every second syllable is accented (stressed), so this is classic iambic pentameter. Since the lines have no regular rhyme scheme, we call it unrhymed iambic pentameter.
The play also has a lot of rhyming couplets (when the endings of two lines rhyme with each other). Check out these lines where Helen convinces the King to let her try to heal his disease:
What I can do can do no hurt to try
Since you set up your rest 'gainst remedy.
Here, remedy is pronounced like remedie. The effect is that Helen sounds a little sing-songy, almost as if she's chanting. (By the way, the witches in Macbeth speak in rhyming couplets when they're casting spells and chanting over their cauldron. We're not saying Helen is a witch, but the language in this scene is definitely a little trance-like, which suggests that her healing powers are sort of mystical.)