Like a lot of Mike Leigh's films: overlong, not a terribly gripping story, superb character study, some brilliant acting mixed in with over the top scenes, delightful period detail. A researcher got her own credit up the front and she deserved it. Timothy Spall was very good as was everyone, really - I'm always delighted by discovering unfamiliar faces in British films (eg Paul Jesson who plays Spall's father). There were some clunky Leigh acting scenes such as the two women bitchily commenting on the paintings, plus Victoria and Albert.
There's a lot of coughing and grunting - I can't recall a movie with more phlegm. Or sex scenes involving old people. My favourite scene was when Turner was finding himself praised by an idiot, who was showering Turner with compliments and bagging out an old time artist. There are plenty of moments like these - a look at the artist as a man: not a horrible person but he neglects his wife and daughters, carries on a second life in a different town, grumpy, touchy, bad diet, few close friends; deals with even touchier rivals.
Fans of painting from this era will love it, as will Leigh/Spall fans. I admired it but was glad when it ended.