It's been a while since I last read it, and I found I'd forgotten most of the descriptive passages. The (Hiawatha-esque) section contrasting the river in good weather, with the river in bad weather was a beautiful piece of writing I thought.
I agree with pdurrant, it shone an interesting light on how things really were in 'good old days'. The bit about children throwing stones at the rowers was described as a pretty normal bit of fun - these days they'd get Anti_Social Behaviour Orders from the authorities (we're lucky that children today are so much better behaved than previous generations
As a literary work, combining other elements as well as the humour - I thought 'Three Men in a Boat' is a deserved classic, and hugely enjoyable.
As a purely comic work, there are funnier examples from (broadly) the same period imho (e.g. 'The Autobiography of Augustus Carp', 'Diary of a Nobody').