These and other sources state or imply that Slevogt was a very important German painter. That is probably so, though I can't work up much enthusiasm for his manner of sketchy brushwork and therefore don't regard him highly.
Your taste may well vary, so here are images of some of his paintings in approximately chronological order to ponder.
The same model seems to be in both paintings.
Around this time, Slevogt's sketchy style kicks in more noticeably.
This might be his wife, Antonie (Nini) Finkler.
More than a sketch, less than a painting.
Berlin's main street shortly before the Great War.