Nice and interesting thread. I've often pondered on how I would've rated a particular game if I were to review it. I still think an evenly laid out 1-10 scale is pretty fitting, but just hasn't been used and perceived in a way that fits my taste.
For me, it would be something like:
1 - Broken and pretty much unplayable.
2 - Playable but boring and not enjoyable in any way.
3 - Has some merits, but has serious flaws that bog it down.
4 - Somewhat OK game, doesn't do much wrong, but lacks any ambition.
5 - Your average game, well playable and even fun, but nothing special.
6 - One of the better games with more individuality and good value, but has issues that impair my enjoyment.
7 - High value game, with no real flaws (for me), but not enough to really wow me.
8 - Excellent game, has some outstanding merits that wowed me.
9 - All-time great, excels in multiple categories.
10 - Near-perfect, excels in all categories.
No real 10 for me so far, but it's definitely doable. That categories BTW are visuals, audio, gameplay and atmosphere. If a game has not enough content, that will also put down the score no matter how good it is.