They have plenty of good source material to work with for at least two more series.
A Game of You, Brief Lives, Worlds End, and Season of Mists were all great graphic novels, as well as a lot of one-offs collected in Preludes and Nocturnes, you can find them online but if you're not used to reading comix you'd probably find it weird.
The last 20 or so issues (Kindly Ones and The Wake) of the comic series weren't as strong as those above.
They change the colour and/or gender of a lot of the characters in the show and it's mostly fine but I'm not buying Mrs. Lucifer.