Actually, a ten shouldn't mean literally perfect - without flaw. It should just mean that it's masterfully done.
That's why we use stars, honestly. People interpret someone giving a game a 10 as saying it is utterly and completely without flaw. Us giving a game five stars, on the other hand? Sure, it's technically the same thing, but if you see a game get 5/5 stars, you don't think "oh, it must be perfect 100%," you just think "damn, that must be a superb game."
Besides, even if the characters ARE fairly stock, they're likable enough, and the story is well
told for all its cliches. I'm not going to spoil Tuesday's review, but it was the first time a Halo game felt genuinely emotional