1 - Mankind is diminished by this movie's very existence. Ex: Human Centepede
2 - Horrible in every way, except that the story is less offensive. Ex: Shark Boy & Lava Girl
3 - Horrible in almost every way and probably a vanity project. Ex: Glitter or Gigli
4 - Usually a comedy that but ends up being irredeemably un-funny. Or an action movie with no internal logic. Or a kids movie with excessive profanity. Ex: Step Brothers/The Other Guys/Ant Bully/Terminator: Salvation/Troy
5 - You could see what they were trying to do, but nothing ended up working and you wanted it to end sooner rather than later(but you end up forgetting about it as soon as you turn it off). Ex: The DaVinci Code
6 - Not awful, but nothing too memorable and/or rewatchable either. Ex: Road To Perdition
7 - Hey! That was pretty good, and in a pinch I'd watch that again and enjoy it as much the 2nd time. Ex: Inglorious Basterds
8 - That was really good and I'll probably buy that one on Blu Ray because I'd watch that a few times. Ex: Memento/Inception, •Pirates of the Caribbean: The Curse of the Black Pearl
9 - I enjoyed that one and clearly that is one of the best movies in the genre. And/or it was likely groundbreaking. Ex: The Matrix, Black Hawk Down, Die Hard, Jaws
10 - Fits the criteria of level 9 rating, but adds something extra that makes it personal to me. Ex: Miller's Crossing, Raiders of the Lost Ark, Star Wars
I guess I was thrown off a bit by your 6.5 is getting into insulting territory. I love seeing what other people's rating systems are. I THINK mine breaks down to something like this:
10/10: One of the best movies of all time - perfect or damn near perfect.
9/10: Great movie. Maybe not GOAT, but one of the best movies that came out that year/best of the decade.
8/10: Damn good movie. Equivalent of making a 'best of the year list' or one of the best of the genre.
7/10: Good movie. One that that I would watch a few more times, or that I like but know isn't that good, so a lot of guilty pleasures end up here.
6/10: Slightly above average. Probably would consider watching it 1-2 more times, but didn't get much out of it.
5/10: Average movie. OK, I got through it, but wouldn't pop it in again.
4/10: Below average movie. I made it through it, didn't like it, but could see something in it that I would still consider suggesting to others
3/10: Bad movie. Got through it, didn't like it, and didn't see anything to warrant suggesting to anybody else.
2/10: damn bad movie - couldn't get through it without using the FF button.
1/10: Terrible movie - had to turn it off.