I have seen paintings with the same style as Henry Rousseau as a kid, and I remember that they appealed to me in a very specefic way. I still have not researched that specific term, but "The Sleeping Gypsy" is the best way for me to describe my feelings about this particular spark.
The painting contains many different factors that together creates a very stimulating image. It is very dreamlike with the color, the environment creates a spurring poetic mood, and most importantly the the smooth surface with rich detail where the central perspective is ommited.
Henry Rousseau was described as a naivist, which means that the artwork is executed with simplicity in its subject matter and technique (SOURCE: google definitions). Personally, I do not think that this definition applies to anything painted on "The Sleeping Gypsy" canvas. The reason for this rather unconveinent name is due to the relevance of the academy. As I understand it, art around Rousseau's time was set in stone; academic art idioms or nothing pretty much, but rather than looking at it with a very rigid perspective one can consider that this is the aftermath of folk art traditions. Here is an example of how folk art traditions can go from exciting, to be revived by Rousseau to what we see in our everyday life.
This examplifies a paraphrase of the real painting projected on a traffic bollard in Winchesterm, England. (SOURCE: Wikipedia images).
This is deliberately an interpreation of the reality that is really hard to imagine, but yet its purspose is to strengthen the painting's emotional expression.
On the other hand, I now understand the rise of naivism that later was shown through artists inspired by Rousseau, like Le Moulin de la Galette by Louis Vivin (circa 1929)
or like Dan le Pre by Camille Bombois (1930)