Well, first off, the issue 21 is the start of the "retooled" PROPHET book. It, along with all of the Liefeld creations, were brought back and given to different creators to revamp. Why they didn't start off with a new #1 is stupid, but I think they were taking the fact that everyone hates it when companies just renumber things and decided to just run with the old numbering ... even though it is almost totally a different story.
Issue 21 is the first issue in this new direction, and boy ... it is new. It is probably the most 'out-there' book I have read, or at least it comes close. The gist is ... one clone of John Prophet has been buried for centuries under the Earth and has now been activated to try and ... well, you will have to read.
You come into this book, if you've never read any of the old Prophet stories, totally out of the loop. Truth is, even if you read the old Prophet stuff this is so different it doesn't matter.
This is not a straight forward sci-fi book. You will not get your Star Trek feel here. This is like reading the old issues of HEAVY METAL. Items and plots are not pointed out to you. You have to both leave your brain at the door and use it more than ever or you will just explode.

I found it utterly fascinating and invigorating for it's unusual take and art that stretches out and takes chances. It is certainly not a book for everyone. Honestly, I would suggest going to CBR and checking out their 4 page previews of past issues to see if you can even enjoy the art before plopping down trade money.
I do know this, as soon as a deluxe sized hard cover comes out, it will be on my shelf!!!!!!
EDIT -
HERE is a preview of the current issue. This is not the regular artist however. I will try and find one with him.
EDIT 2 -
HERE is a preview of #22. Love the unfinished, hectic look of the art in this environment.