Holy fuck reserve S rank for things that really deserve it, at least half of the recommendations made thus far are "X random movie that I love for S rank".
Frozen I love and have seen at least five times in full but it is not one of the best movies I have ever seen or even in the top ten; I would put it in the "A" tier (which btw should mean an incredible recommendation except that everyone else is grade-inflating so massively).
In no particular order:
Beauty and the Beast: B+. Very strong, memorable movie with one real shortcoming: it's villain (Gaston) is at best an average Disney villain, and doesn't hold a candle to the likes of Scar or Frollo.
The Little Mermaid: B. Personally, I always found this movie to be very drawn-out and boring for long periods. Some of the songs in it are among Disney's best, however, and much of the supporting cast is top-tier.
The Incredibles: A. A movie I could watch over and over again and never get bored, it suffers a bit from Death Star/Stormtrooper syndrome (heh get it) in that there is an overwhelming arsenal of weapons and personal at the disposal of the villain that never really amounts to anything.
Frozen: A. The best animated movie in a decade (since The Incredibles, in my opinion), and also possibly the most unique Disney movie ever. The music is like something from an S ranked film and the characters/plot are both compelling and powerful. The reason I do not give this a higher rating is that I did not at all buy into Anna's character until at least half way through the movie, and felt that her (small spoiler alert) 'fight' with her sister in front of everyone at the coronation after party was very forced in terms of moving the plot along; I feel that with a royal upbringing the various attendants who presumably helped raise her (not to mention her parents before their death) would have ensured she had a better understanding of her duties, as Elsa did. A small quibble but considering the entire plot hinges on this point and that Anna is the main character and I found her the least compelling of any major character in the movie, I feel it is not too much of a stretch.
Aladdin: A-. In the same vein as Beauty and the Beast, it has a fantastic score and supporting cast, with the difference being that Jafar is in my opinion a stronger villain than Gaston, and that Robin Williams as the Genie outstrips any of the characters in Beauty and the Beast in terms of sheer screen presence (in terms of personality; there's really no beating the Beast in terms of screen presence physically :O)
Pochahantas: C-. My god there are so many problems with this movie...I didn't feel much of a connection with any of the characters or anything they were doing, and the villain I literally cannot even recall the name of (Governor something I think, idk he was fat and greedy or something). Manages to avoid a complete fail because if this movie didn't exist than Colors of the Wind would also not exist, and that song is one of my personal top five favorites in any Disney movie.
Tangled: C-. Am I going to be the only one to say it? Tangled was a bad movie. The premise was preposterous, the characters were caricatures of more interesting characters of past Disney movies, Flynn Rider couldn't figure out whether he was a hero, villain, or thief with a heart of gold (at least Aladdin stayed consistent the entire time), and apart from one very powerful scene near the very end of the movie when (spoilers) Rider 'dies' (a scene which lifts this movie just out of failing), they somehow manage to fuck that up too by randomly making her tears heal things as well in order to get a happy ending. This movie would've actually gotten a B- (I kid not) if it had kept him dead, because at least then it would've done SOMETHING original or thought-provoking. Her relationship with her kidnapper/fostermother the witch is a pale imitation of the relationship shared by Frollo and the Hunchback in Notre Dame, and one I never bought whatsoever. Last point: the 'scene' in which she tries to stuff Flynn's unconscious body into a wardrobe is one of the worst scenes I have seen in any film, ever.
Finding Nemo: B. Yes it is an engaging story, but honestly there wasn't anything that stood out to me. I cared about the father, the opening scene was a heart-wrencher, and I was never bored but...it just doesn't quite rise to the level of many of the aforementioned movies (again, with the exception of the opening scene).
Cars: B-. The Pixar movie everyone hated on until Pixar started making bad movies with regularity...I bought the weird as hell premise (ie that everyone is a car) and I bought the main character's development (though I found him incredibly annoying to start...I guess that's sort of the point though?). Lack of much of an interesting villain (I cannot recall the rival car's name even or one line he had) or much tension at all throughout the movie made it run a little dry at times, and, again, there was no single 'great' scene in it.
Toy Story: A+. A classic, open and shut. The entire main cast is memorable, the dialogue is witty and engaging, and the difficulties facing them are incredibly hazardous for toys (and I really cared what happened). Not my absolute favorite because while Sid is malicious and serves his purpose perfectly well, there is no real evil 'force' at work; the only evil forces are Sid's whims, which isn't as engaging as a story with a truly dangerous enemy.
The Hunchback of Notre Dame: C+. Poor Claude Frollo...possibly the best, most realistic, and consequently most disturbing villain in a main stream animated movie, and he gets stuck in this hodgepodge of a 'retelling' of a classic that tries to avoid most or all of the powerful themes that the novel it purports to be based on explores. Disney punts on taking on religion, punts on any serious dealings with the perversity of human nature in either Frollo or the Hunchback, and instead makes it a cut-and-dried 'racism against the gypsies' tale where the most attractive male in the story ends up with the most attractive female in the story and the villain pays for his misdeeds while everyone else gets a happy ending. I don't even bother to say spoiler alert for this one because it was so goddamned predictable. Still, 'Hellfire' is another on the top five list of Disney songs, and many of the scenes between Frollo and the Hunchback are incredibly compelling.
Tarzan: C+. I didn't find Phil Collins' soundtrack all that memorable (although I'm aware I'm in the minority on that count), and I didn't think any of the characters were all that interesting. Nevertheless, it is an engaging tale and one I wasn't ever finding myself questioning, so I guess it is as 'meh' as it comes for me (and yes, 'meh' should be a high C, at best).
Mulan: B-. Let's get this out of the way first: 'I'll Make a Man Out of You' is another song on my top five list. And, yes, Mulan is a compelling character who deals with a difficult, realistic situation as well as she can, and grows from it. However, the villainous forces are so bland (the Huns are just this raw destructive force that don't even speak as far as I can remember, though that one super muscular guy seems to be at least cognizant of his surroundings, while that annoying fucker who demands Mulan be executed when it's discovered she is a woman is such a forced 'let's introduce sexism as a theme into this movie' character...) and the ending is so mundane that it's hard not to think of this movie in very black and white terms. The opening is amazing, it has one of the best songs of any movie, and the avalanche scene will stick with me forever, but much of the rest of it is just so bad that it's hard for me to call it a 'good' movie so much as a missed opportunity.
Toy Story 2: B. The worst of the Toy Story movies by far, as well as easily the most preposterous. It is still a compelling story that I cared about the entire way, and I still for some reason remember the ending in the airport vividly even though honestly it's not a very strong ending, but as weird as it sounds, I miss Sid in comparison to fat sheriff and that slimeball collector. The supporting cast remains excellent, though there is less for them to do in this movie than in either of the installments before or after.
Toy Story 3: A-. The funniest of the three (for the first half), it requires a bit of a leap to get them to the school but once there, it feels almost like something out of "One Flew Over a Cuckoo's Nest". That feeling of being trapped comes out so well in this movie, and fuck that teddy bear. The ending was really sappy and drawn-out, and there I felt as though Tom Hanks sorta phoned it in on this one, as did the writers who wrote Woody's lines...he just felt uninspired in comparison to either of the first two.
And obviously, the one I've been purposefully saving for last:
The Lion King: S. This is the best Disney movie ever, and my personal favorite animated film ever. The intro sequence is one of the best sequences in any movie across any format. Scar is a Shakespearean-esque villain. Timon and Pumba are the best comic relief characters in any animated movie because they are real and are not just there to elicit laughter. The entire supporting cast is memorable. The music is as complete as it is in any Disney movie, as 'The Circle of Life', 'Hakuna Matata', 'I Just Can't Wait to be King', 'Be Prepared', and 'Can You Feel the Love Tonight' would all be the best song in almost any other Disney movie. The only small regret I have is that 'He Lives in You' was not written until after this was released (for the Broadway musical, which I highly recommend to anyone with the chance to go), and so was relegated to the opening credits of 'The Lion King 2', a movie I have not seen in full nor ever plan on seeing lest my impression of the first be tainted. I've occasionally wanted to re-watch other movies more (Frozen most recently), but in the long run if there is any animated movie that will stand the test of time, I am confident it will be The Lion King.
Finally, my choices for five best songs:
1. Circle of Life ('The Lion King')
2. Hellfire ('The Hunchback of Notre Dame')
3. Let It Go ('Frozen')
4. I'll Make a Man Out of You ('Mulan')
5. Colors of the Wind ('Pochahantas')
Honorable mentions: 'Tale as Old as Time' ('Beauty and the Beast'), 'Hakuna Matata' ('The Lion King'), 'A Whole New World' ('Aladdin')