A not so poetic demon
I was going to do this whole thing in rhyme, but I'm just not that good at this time. Demon Knights is not well written for a comic book. It seems to me that the writer wanted to use several cheap techniques he stole from Screen play writing. They don't work in comics the same way. They art is basic and doesn't break the mold at all. What you would expect from an Etrigan centered book is what you get.
That being said the general pace of the book, the introduction of lore, and the several characters introduced were more or less done adequately. Vandal Savage seems off, but he's been around for a while so he might have changed over the years.
My only real complaint as far as why someone who like Etrigan or one of the several characters also introduced that might not be in there a long time (Xanadu, Mordruu, Morigan Le Feye [name not stated, but presumed], The Shining Knight, and Vandal Savage) is that Etrigan doesn't do the thing he is known for. I always thought that the rhyming was natural to him since his origins so that he hasn't rhymed yet looks like the writer couldn't do it or something...
edit: Another complaint is that the story takes place starts 400 YA (1600s) and then jumps AT LEAST 90 years ahead place it in at least the late 1600s to early 1700s. The dark ages were 400s-1400s. The Renaissance happened between the 1400s and 1600s, and if that 90 year jumps was more than a few years after the 1600CE mark it would place these guys at pretty much the beginning of the American Revolution and as it is well into colonial america and the British Empire era. This writer needs to learn some history.
This isn't a disaster but it's nothing special either. Given the characters it could get better later and you'll want to pick up this when it does so if you have any interest in Etrigan, or the characters I listed, pick up the book. Otherwise, you can pass on this.