Oh, I'm all over the opposite of sub-9 = crap. If I was to rate games, people would think I hate everything. However, it's just that I operate on a different scale than most. I think that the problem with this is that people treat game scores the same way they treat grades in school, so the ratings system becomes a total mess. In school, you get an "F" if you get less than a 60% (it was under 70% for my school, but it's an exception). So people see that if you're under 60% with a game, it's an utter failure.
Because of this, you see the outpouring of 9's and 10's by reviewers. If you like something, you give it a 10. If you don't, you give it a 7. If you are a fanboy, 1. In my opinion, this isn't the way it should work. When we're talking that 1-10 scale, I think that you need to be able to use the entire scale, or the scale itself serves no purpose. As such, I consider "5" to be average. If I give something more than a 5, I'd probably say it's worthwhile to play. Under that, I'd say it's probably more based on preference (unless you get to a 2 or something). I really like Black Ops II but I'd probably give it a 6/10. I love Skyrim, but I'd probably give it a 7 or 8, because I don't think it's got a lot of replay value, the difficulty scaling isn't very good, and it's got a good number of bugs. I can't think of a single game I'd throw a 10 at.
But like I said, I blame schools for the broken rating system. When you're raised being told that average is 70%, and failure is 50%, you're going to carry that mindset with you--mostly because it makes sense, in a lot of cases. You can't do half of your job and expect things to work out, haha. If a doctor knows half of what is wrong with a patient, how's that going to go? You NEED to be in that 90% success rate territory.
For entertainment, that doesn't need to apply. If the game is functionally sound, then you need should primarily be judging personal preference here. If you think something is an "average" game, why not take the "average" point on the scale, a 5/10?