Ensor's imagery is very nightmarish. Characters have faces that resemble masks, demons taunt and torment people in a variety of ways. There's always some sinister character or act set forth in his work. Apart from his disturbing masked characters which he is most well known for, he was also a master at depicting architecture, as can be seen in this etching.
5th Gallery - Check out the first picture in this gallery. The image is huge and lets you really study Ensor's mark making.