If we're talking reviews aimed towards readers (opposed to critique-oriented reviews for creators), I think the most important criteria is whether or not you found the comic enjoyable. So, that doesn't need to be bound to a strict metric that applies to every single comic; just focusing on the pros and cons of a comic on a case-by-case basis is fine. I'm more interested in hearing what did or didn't appeal to a reviewer, than having each comic put through the same exact rubric over and over. A less formulaic system also makes for more interesting reviews, I think.
Of course, there's going to be criteria that applies to every comic like art and writing, but more specific stuff doesn't have to apply to each and every review. For instance, pacing is a common element but it won't apply to gag-a-days, so no harm leaving it out in those instances.