plus at the end of the day, I have a hard time reviewing things if I can't be fair to it. Like I would have never written a review of Scott Pilgrim volume six, because I knew that the concept was not for me, but more importantly, I knew that the way it played out would be at least okay to the target audience.
a miniseries is a graphic novel for all intents and purposes. to review issue 5 and not issue 1-4 and 6 or to go into it without the knowledge of what happens in 1-4 is unfair to the book. It is like picking up a random novel turning to page 322 and reviewing the next twenty pages but never looking at the rest of the book.
If we were doing old school comics, you would at least get a feel for the book from one issue. However, that is not the case with a modern book.
Of course, I am not espousing that everyone do that, they can review however they want.