At the risk of sounding like a philistine I have to say that this is not one of Keat's finest. It lacks assonance and the rhyme is extremely forced. He might have scribbled this on the back of a Greek Urn while he was waiting for Autumn. Sorry.
The fanciful roaming indeed gives joy of freedom as detailed by Keats! This reminds me of John Milton's L 'Allegro and Il Pensareso making survey of the world in Nature and human life fancifully and philosophically in wonderful immortal poems of all times!
A beautiful poem by Keats, obviously inspired by Milton's poem duo L'Allegro
and Il Penseroso. i; m much more inspired by the first stanza than the second, but just like in Milton's duo of poems, this seems to be portraying two different types of fancy for two different types of people.
'These delights if thou canst give,
Mirth, with thee I mean to live.'