Keats was just 25 when he died, in 1821, but there is no argument whatsoever about his reputation. The work he produced in his few years of poetic effusion is almost universally considered outstanding.
It is easy to understand why, if one considers only the great Odes on which largely his reputation rests. There is a unity of tone in all of them, but the subject matter that rouses his melancholia differs widely. The Grecian Urn is an inanimate object, of beauty, but also of animation, which allows a characteristic perception
Heard melodies are sweet, but those unheard
Are sweeter; therefore, ye soft pipes, play on;
Not to the sensual ear, but, more endear’d,
Pipe to the spirit ditties of no tone: