The idea is that if I set a game on the first 3 ratings then it's a bad game. It's not worth buying unless you really must buy that game. If I put it on the 3 last ratings then it's a good game that more and more deserves your money.
For example. Deus Ex is currently the only game to get a perfect 6/6 score. This doesn't mean that only one game can get 6/6 or that the game have to be completely perfect. The game have to be fun, serious, deep and have a solid story. More or less.
I compare all games I review with every game I have, not only recent games like all other reviewers does. Which really puts the bar quite high but damnit, we're serious gamers and we deserve high quality entertainment on our computers!
For my Dragon Age review I compared it with Neverwinter Nights 2, Mass Effect and Baldur's Gate 2 for example. These are all Bioware games and I compare their best features and analyse if the game is a step forward or back. If they don't make any improvements on their games then they become very generic. That's bad because then you don't get anything new and that's one of Dragon Age biggest problems. The plot is unique and so is the combat system... but not unique enough. It isn't developed or explained as it should be and that's why the game is so bad. If you're going to make a difficult game, make it at least very familiar or long or incredible amounts of replay value. But come on, a roleplaying game is often not supposed to have replay value. It's supposed to have content.