Learn English – Does “goodly” in this sentence in Hamlet mean “considerable” or “pleasing

It’s still acting as a modal verb here; this is an ellipsis for

I must [go] to England.

The OED glosses this usage, under the main sense of “expressing necessity,” as “(b) With verb of motion understood. Now arch.”.

(Must does also have some non-modal usages: “to become mouldy, musty, or mildewed”; “to dress or dust with hair-powder”; “of a male elephant, etc.: to come into a state of musth”. But I suspect none of these is what you, or Hamlet, meant.)

Edit: an earlier version of this answer described this instead as the OED’s “(c) with implied infinitive taken from the context,” which arguably fits, but I think the more specific (b) is probably more apposite here.

I understand it to mean both of those things. Shakespeare managed to pack a lot of meaning into his words. He would have been aware of all the possible senses.

If you wish to answer the question for yourself, think about what the nature of heart is in metaphor.

If we set aside science and medicine, the word 'heart' is most often used in relation to love and to courage.

The following website archives many sayings about the heart.

Heart Quotes and Proverbs

http://heartquotes.com/Heart-quotes.html

ADDENDUM

The word 'courage' derives ultimately from the Latin 'cor' meaning 'heart'.

courage (n.) Look up courage at Dictionary.comc. 1300, from Old French corage (12c., Modern French courage) "heart, innermost feelings; temper," from Vulgar Latin *coraticum (source of Italian coraggio, Spanish coraje), from Latin cor "heart," from PIE root *kerd- (1) "heart" (see heart (n.)) which remains a common metaphor for inner strength. In Middle English, used broadly for "what is in one's mind or thoughts," hence "bravery," but also "wrath, pride, confidence, lustiness," or any sort of inclination. Replaced Old English ellen, which also meant "zeal, strength."