I strictly write my reviews on the basis of:
If you don't have anything nice to say, don't say anything.
The reason for this is because this blog was never put up for the sole purpose of reviewing books. It takes TIME to read a book, and writing reviews takes quite a while, too. A lot of thought goes into them all. And I don't know about you, but any form of thinking requires that valuable thing called TIME.
Considering that I do have little of this valuable thing on my hands, I only write reviews about those books that actually kept me enthralled - which is no mean feat, because my attention span can be lacking at times (even my teachers used to complain about that). So really, my reviews are meant to be seen as recommendations.
I wouldn't bore my friends by telling them how much I didn't like a book, but I do tell them what I think they might enjoy. So why should it be any different online?