A lot of it can be to do with your target market too. For example, if you're aiming towards new players to online poker, you can afford to be a bit more "exaggerative" when writing reviews about the poker rooms you want the most players at, as chances are they have very little, if any online poker knowledge.
But if it's players who have played online - even a little bit, you have to be more honest in my opinion. You should also make your reviews as factual as possible, and anything that may be deemed controversial, back it up with facts. Like lets use Full Tilt Poker as an example - I've played there a lot. I've never had a problem with support, whether it be the affiliate department, general support, tech support, or cashier support. However I read a lot of poker forums, and I see Full Tilt getting quite a lot of bad feedback. So how do I handle this? If I write "Full Tilt are the best support on the internet! Never a bad experience!" and one of my readers, and potential customers, has read any other forums or even experienced this first-hand, he might think "Hey - thats BS, I've read they have bad support! I can't trust anything this site says" and boom, closes it. So in situations like that you have to be careful, say that you haven't had any problems at all, but others have.
I fully believe honest reviews are the best way to go. Of course, that's not saying that you don't embellish, exaggerate or even stay away from particular details to users. For example I might want to advertise a $1000 signup bonus that a casino is doing, and not mention that the requirements for it are horrible. Of course, again, it all depends on my target market. If my target market was casino bonus whores, then of course I would have to mention the requirements.
