When I contemplate the purchase of a new title I now find myself sampling a selection of reviews good and bad (trying my best to avoid spoilers along the way) and trying to decipher whether those other readers (and sometime reviewers) share my taste and my values. My best method of trusting another reviewer is to check out how they reviewed books I have loved. If they loved them too I take a punt that we are sympathetic and I trust their judgement to help ME find books I might enjoy. You might see their reviews very differently. You might be looking for different things. That's cool. I find it very helpful if reviewers have justified their position with specific examples (although not if you haven't read the book yet - potentially very spoilery). If they rant without justification this is also informative - these kinds of reviews can make for fun reading but are less likely to give me a real feel for the quality or lack thereof in a particular book. But a gut reaction can be just as meaningful. Over time you can build patterns and find some terrific books.
The bottom line is if you don't agree with what a reader has said in their review, this does NOT mean they are wrong. The biggest mystery to me is writers I love, who praise other writers whose writing is just not in the same league. And then you begin to question their impartiality. Which opens up the whole impartial worms can. It's a big can. I'm not sure anyone can ever be truly impartial. Everyone has an agenda, whether it's to support their writer friends, further their own reviewing career, or vent from their soapbox. Wondering about motives can mess with your head. DON'T do it! DO be as honest as you can be in your own reviews. DON'T review books you haven't read. DO respect the opinions of others. If you can, it can be helpful if you can justify your position/opinion - this can be a good way to develop your own reviewing skills. But folks at the end of the day your gut reaction/visceral response alone IS enough. I saw Iron Man 3 recently. I wanted to love it but I didn't feel the same level of satisfaction I felt after watching The Avengers or Dark Knight Rises. I enjoyed the movie but that ultimate gut satisfaction just wasn't there. You can't pretend that reaction. And the books that leave you with that profound sense of satisfaction, or that move you or transform you - they are the ones you should rave about. And you want to be free to say whether they do or don't, don't you?