Carl Friesen on his four tests on the usefulness of a 'review' article can be applied to pretty much all comment blog formats.
- is it relevant to the audience?
- do you know a lot about it? does your experience cover this topic?
- does your opinion have weight? are you qualified in this area?
- has this particular topic been 'reviewed' to death? In most niche aspects of knowledge businesses the answer is, fortunately, 'no'.
So if you are a qualified professional, discussing topics on your 'home turf' then really all you need to worry about is Number 1: Is it relevant?