There is plenty of information floating about the internet on this subject, so no need for too much detail. Their art department produced some of the best art pottery of the late 19th century employing artist such as Hannah Barlow, Florence Barlow, Frank Butler, Mark Marshall, George Tinworth, Eliza Simmance to name a few.
Sadly; the demand for good Doulton stoneware items has declined in recent years. I think that the good artist decorated pieces like the above have got swamped by the ordinary and boring production items that remain on dealers shelves unsold and unloved.
A much written on subject - here are a few.