What makes a good game review?

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What do think is essencial in the reviewing of a game? It happens often in commercial reviews that they need to give the game a good review or the reviewer will not get the free merchandise from the game publishers in the future but doesn't that throw out the whole point? I particularly like the reviews in Zero Punctuation. The game is entirely ripped to shreds so at the end of the review you know exactly what is good about the game as well as what is bad about the game. Isn't that what a review is supposed to be all about?