Here is van Rysselberghe's Wikipedia entry. It is much more comprehensive than many other artist biographies I've linked to recently, so you might as well refer to it for details of his life and career.
So far as van Rysselberghe's painting styles are concerned, I would say that he began his career as a conventional representational painter, circa the early 1880s. That is, his style was more free, more painterly than what hard-core academic painters would use. As the entry above indicates, he discovered Impressionist painting and then the Pointillism of Seurat and soon becoming friends with others working in that style. However, van Rysselberghe usually tempered Pointillism, especially when painting portraits or otherwise incorporating people in his images. That is, faces were painted using more conventional brushwork. Many such paintings were made in the early 1900s when he was drifting away from Pointillism, so perhaps those faces served as part of the transformation mechanism. After 1910 his paintings were still brightly done, but had returned to more conventional brushwork. Van Rysselberghe does not seem to have indulged in any of the avant-garde styles that appeared in the decade or two before the Great War.
Setting the scene, here are portraits of a good friend of van Rysselberghe painted 23 years apart. The 1892 painting is strongly Pointillist, even extending to the subject's face. The later portrait is essentially conventional.
Van Rysselberghe made three trips to Morocco, a place that fascinated him for several years. The work above seems to be more than a quick sketch, but is less detailed than some of his larger Moroccan paintings of that time.
A Pointillist landscape. I cannot find a date for it, though it was probably painted around 1899.
These are examples of paintings with Pointillist or Divisionist backgrounds and where subjects got a more conventional treatment,
Here van Rysselberghe is returning to conventional representation.
This was painted a few years before he died, when female nudes were a favorite subject for him.