David's basic style was what has been derisively termed "Pompier" in reference to the Greek-style helmets worn by Parisian firefighters. This had to do with subject matter and the idealized depictions done in a highly "finished," hard-edge manner. More regarding his evolution can be found at the above link.
Given his political stances, David was reluctant to work in France following the Bourbon restoration. Having fled to what is now Belgium after Napoleon's fall, he remained in Brussels for the last years of his life.
Although David remained capable of making Pompier works during this time, some casual paintings of a greatly different character survive. I found two examples in December at San Francisco's Legion of Honor museum.
According to Wikipedia, this is David's last Pompier painting.
A portrait of one of his twin daughters. Napoleon was still in power and David was still in Paris. But at age 64 this can be considered a late work.
Close-up view. This seems to be little more that a sketch or study. Or might have David anticipated artistic trends 50 years in the future? Probably not, but I don't know enough to be categorical about this.
This was painted the same year as the Mars and Venus painting, within two years of David's death. Again, the style is casual and sketchy. Could this have been a study for a more finished work that was never made? Again, I don't know.
A slightly closer view.