Oho! A discussion thread. Time to generate words in a meaningful-sounding order.
The best reviews, I think, go through an entire chapter, or more than one chapter, and variously point out incoherencies, typographical errors, deficiencies of character, stylistic lapses - and provide helpful suggestions for ways to improve them. Those are the flavour of review I try to leave, which is one reason why I review so little; I can't bring myself to leave a shorter review if I know there's more I could say that might help, and so only sit down to review when I know I have an uninterrupted hour or two to work in. This is not admirable, and I really do need to leave reviews and responses more frequently.
Oh, and I like to make jokes. That's not just part of reviewing, it's more of a pathological obsession that means I can't write for longer than a few minutes without resorting to humour and/or haiku.
Fairly unsurprisingly, the sort of reviews I give are the same kind I like to receive; if they're going to help me improve, then they're worthwhile. In addition, if the person reviewing appears to have a sense of humour, that sweetens the deal immensely. Having said that, I also don't mind getting shorter, less in-depth replies - what I would call 'responses', rather than 'reviews'. It's just nice to know that someone is reading and enjoying my turgid output of prose; entertaining others is, after all, my basic aim as a writer.
If we're going to create a new Reviewer's Guide, the first thing we'd better do is make sure the title isn't misspelled (cough cough, look at your first post, bobandbill, cough cough). After that, we can get down to content. You know, I don't actually recall ever seeing a reviewing guide here on PC, and a quick search of the forum for 'review guide' reveals nothing at all relevant within the first 50 results, so I've got no idea what our previous one was like. However, as well as laying out the etiquette of reviewing and suchlike that you'd expect of such a guide, I think it should definitely make it clear that both short 'responses' and longer 'reviews' are allowed in these forums, not just the latter. I agree with Phantom that there may well be some who are put off posting even just the former here, given that the bulk of the reviews being written currently here are the longer, more in-depth sort, and any new Reviewer's Guide needs to clearly state - perhaps even with an example, to make it as obvious as possible - that shorter reviews are acceptable as well.
EDIT: I just found the old Reviewing Guide. Though I was stupid to have overlooked it, it was... definitely too out of the way to be of that much use. I think it needs its own thread, at the very least, rather than being buried under a mountain of other resources.