A
Brilliant; accepted definition applies: absolute makings of a masterpiece; no longer a show pony meant to correct misconceptions about said film by overextending grade's weight; the so-called perfect film (whatever that means); used infrequently to describe a movie whose flaws are either nonexistent or highly justifiable (so much so, that you know of but are refusing to read many essays written on the subject of said flaws); usually granted exclusively to previously 'A-' films seen a second time; rare instances of use on pioneer viewing usually coincide with film's status (i.e. - its a classic film released in an era before mine, its holds an absolutely unmistakable or frequently interesting subjectivity personal to reviewer; a honest to goodness mood changer (from any mood to highly elated).
(perfect example: Memento, Christopher Nolan)
A-
The next rung following a fairly common occurrence called "exceeding one's expectations" (almost always done on second viewing); the great not good factor (preceding the above use of the word brilliant); a revelation previously nestled between B and C; a movie you suspect will be a repeat viewing/light guilty pleasure.
(perfect example: The Man Who Wasn't There, Joel Coen)
B+
A rare gift for films that exceed expectations; don't fit in the category of "good" comfortably; movies you flipped over (A-, occasionally A) and have seen again in a more objective state of mind, perhaps; a place many, many foreign films that would probably have landed much higher (were you only fluent in their native tongue).
(perfect example: In the Mood For Love, Wong Kar-wai)
Accepted definition of unmistakable quality better expressed as good not great; an otherwise great film is marred by a debatable flaw you just can't seem to ignore; an otherwise solid but not really intriguing or beguiling film you find yourself equally unable to punish or praise; sorry to say, but the recipient of this grade often starts with a wan first act, more concerned with exposition than storytelling (usually followed by great storytelling that required a comparatively more complex groundwork or buildup); the words are: perfectly serviceable; it was based on a play.
(perfect example: Ocean's Eleven, Steven Soderbergh)
B-
A throwaway; more often than not, its effectively forgettable entertainment (a film people will have to repeatedly remind you that you've actually seen); where a movie you previously graded higher usually stops on its way downward (as the subsequent days build relentless doubt through your privileged "outside the theater" perspective); sometimes, when it's not forgettable, it's a film you really have to sell your review in order to comfortably sit on the fence (i.e. - you find yourself justifying your own comments thoroughly because, as a middle of the road movie, it's less likely to be a lopsided approval rating - these are those movies you are warned about, the ones that are open to interpretation); put quite simply: you know you enjoyed it but you also know it's not a very good film, making this a limbo for bad movies we love.
(perfect example: A Knight's Tale, Brian Helgeland)
C+
More often than not, these films are the best marketed because they are the most mis-marketed, (they're so appealing for such a variety of reasons, you often start enthused and the experience burns itself out real quick); a film with a great first act and a really wilted second and third act; There's an audacity to the subject matter or the mere release of the film that can be commended - despite lack of actual quality - with a plus (that is, if you're a political reviewer); All your friends say it's good, but, as usual, they're wrong.
(perfect example: Vanilla Sky, Cameron Crowe)
C
First and foremost: dry, boring, dull, indolent films tend to be placed here real quickly and real painlessly; a film with a good first act and a really strained second and third act; in the past it was a B or even a B-, but this time, it's hard to admit you once though so (what a relief when it lands here, in C territory); it placed rather high on a weekend top ten grossing movies list (i.e. - special effects, egos and overkill ad campaign in full effect); Better to have here than have neither here nor there and if you had you'd been a contributor to the artistic process, you'd be less distracted by the there part.
(perfect example: Evolution, Ivan Reitman)
C-
A film with a decent act, but its not usually the one you expect it to be and its almost always decent because the other two are so disappointing (you know, when they show you the gun in the first act and then it damn well fails to go off in the third); there is a trajectory here where a movie burns out extra fast - sometimes in the first reel - and from then on, it bugs you a little more every subsequent reel; funny movies that, for whatever reason, aren't fucking funny in the least; insulting to one's intelligence more than twice (without compensation of nudity); a movie being universally overpraised by every last critic you once trusted only last week but have promptly banned (and also, you've seen it twice, attempting in vain to find something you don't loathe about it); a terrific premise is derailed when the film puts more effort into sucking than into not sucking.
(perfect example: Captain Corelli's Mandolin, John Madden)
D+
This table reserved for movies which are so unbelievably bad that we have a good time watching them merely to laugh at them rather than with them; most of the actors are so outwardly straining to be funny that it is almost painful to watch; looks like the editor's vision, not the filmmakers'; paychecks were clearly needed by a cast you wouldn't expect in a film this bad; a great work of literature is tarnished - but at least you got to spend some time with that great work of literature (because, let's face it, you're not going to re-read the book).
(perfect example: Domestic Disturbance, Harold Becker)
D
It's utter incompetence (and you know it), but an effort was made to dress up obvious incompetence as mere boobery; there was something incoherent or really, really (like last week) familiar about the story being told (not a bad genre piece, per se - but maybe a bad sub-genre piece); the filmmakers tried not to make it public that the film was going straight-to-video or banned-to-cable and finally landed a major star (probably after a paycheck - differs from D+ paycheck comment); a summer movie that burned out in a week or two, hit video with more units than necessary and, when you finally see it doesn't live up to your already lowered expectations; a franchise that doesn't use numbers for its sequels but, nevertheless, has passed its third sequel.
(perfect example: Tomb Raider, Simon West)
D-
Just torturously bad (a terrible film: "Oh, I get it. Don't worry, I get it. It's just fucking awful.); a movie you all the sudden realize has stolen very, very flamboyantly from another film; a movie with ten good minutes - no more, no less; a movie where the dialogue is either boring or so absolutely ridiculous that you can't pay attention to it and, an hour later, you're still unsure what's going on - and why; Because you have to delineate between the D- and the F movies (or, movie, there's frequently only one in the F coffin to stand as the absolute worst film of the year, one that makes the D- movies look almost tolerable by comparison); There's a moment during the film where you realize it's not only going to get worse, but it's going to be borderline traumatizing for you and your companion (at which time you glance at your watch only to realize there's a whole lot more left than you'd imagined); a movie you expected to be a "D+ laughing at it, not with it" affair that turned out to be too wretched to inspire anything more than pure, unadulterated hatred; a franchise that uses or doesn't use numbers for its sequels and passes the third in a series.
(perfect example: Sugar & Spice, Francine McDougall )
F
I turned off the film before it ended (this has happened only twice as I find it more rewarding to slap an F on a film I stuck with than one I didn't); film didn't make any sense whatsoever at any point and therefore, didn't fulfill its only real prerequisite (this goes double for mega-abstract pieces that are so obtuse that you can't even feel anything about them afterwards - because they were so, I don't know, abstract); Movie actually made the rest of my day bad because I watched it (the most rare occurrence on this page, thankfully); the storytelling method requires a circular pattern that (inexplicably) occurs more than once (or, the director was Edward Burns); a franchise that makes its way north of a fifth sequel.
(perfect example: Soul Survivors, I forget)