Dude, I don't think you can give a game a 9 because it has good gameplay in spite of an abysmal story, when cutscenes literally account for HALF THE GAME. Maybe if the game wasn't story driven, it'd be fine, but it sounds like it clearly is, even to a further extent than most games, so when said story, dialogue, and characters are awful, it should have a serious impact on the game! From how prominent you're saying the narrative is, it should be at least as integral to the game's overall quality as the gameplay, considering you apparently spend as much time sitting through FMVs as you do playing the game. I haven't even played it, but going by what you're saying about how big a role story played in the game, and the quality of it, a flat 7 or something probably would've been a lot more appropriate. Going "well the game is clearly story-driven and the story blows but 9/10!!" seems odd to me!
Because, and I know this may be difficult for you to comprehend, it is a fun game. Not every cutscene is poorly written and campy but despite that fact you can still play this game without knowing squat about the story and skip the cutscenes.
You can't do the same with an RPG.
This game takes about 10 hours to complete minus the cinematics plus all the hidden extras plus the great online mode plus the downloadable content. You also have a wide variety of enemies, environments, weapons, and various situations which help spice up the gameplay.
An RPG is atleast 20-40 hours of mashing X, talking to NPCs, and leveling up.
It may be a story driven game but the gameplay is the focal point of the title and the game is, well, fun. I could play MGO by itself and feel like I'm getting my money's worth.
If you don't plan on playing MGO one might feel a bit ripped off but when I rate games I try to look at all the mitigating factors and piece them together. Pacing issues and golden age comic book villains aside, the
game itself is top notch thus the writing doesn't adversely affect my enjoyment. I still penalize it for its pandering but I'm not going to tell my buddy "Hey, don't buy this game. It's really fun but the writing is juvenile THUS YOU WILL HATE EVERY ASPECT!!!"
But an RPG thrives on the plot and writing and the gameplay is almost always second. In the case where the entire game balances on whether or not I can stay interested by reading massive amounts of text, the final score will be lowered dramatically but the beauty of MGS4 is that you can press START+SELECT and still enjoy the game.