Field was not a natural composer and ideas did not appear to have exactly flooded through his pen. He often only composed when he needed to (upcoming concert) and his drinking did not assist in his later years.
Out of all of his works, i feel perhaps the concerto's are the most satisfying (or for me at least). I have read through all of them and have a particular liking for 1st, 5th & 6th. The sonatas are perhaps too "Clementistic" and the collection of rondos and variations composed to please the Russian nobility, perhaps are no longer attractive to modern ears.
His Nocturnes are a good stepping stone for those of Chopin.
Thal