You know a scoring system is completely broken when 6/10 means it sucks.
Actually, the problem isn't with the scoring system. It is with us. We are more picky when it comes to expensive games. Well, I don't see it as a problem. It is just how it is.
6/10 still means the game is slightly above average, but for our $50, anything less than a 9 or an 8 isn't worth it. So while the scores aren't saying the game sucks, and are saying it is only above average, we as consumers feel it sucks and is DOA.
Basically, the thing is that when it comes to 'AAA' games which are sold at $50-$60, anything less than excellent is not worth buying, and thus 'sucks'.
So essentially, while 6/10 might be a very just score for this game, to be fair, anything less than an 8 means the same thing for an AAA game.
The game actually doesn't suck. If you read the reviews, the game is OK. The problem is that we just expect AAA games to be so good that they deserve a score of 9/10. If not, they are a disappointment.
I think the reason is that unlike movies, where you can still happily pass the time for $5-$10 at an average movie, a triple A game is a bigger investment in terms of money and time, so it has to be amazing.
The reason I don't think this is a problem is because the gaming landscape has changed. Thanks to PSN, XBL, Steam, and mobile gaming, you have a ton of indie games that cost a few bucks and are worth buying even if they are a 7/10 because they are so cheap. This means that developers who don't want to take a risk can freely make games for such markets.
On the other hand, you still have big budget games like Thief 4, and the risks the studios take with these is that they have to make the games really awesome, or risk failure.