I grew up watching this film as a child, and I remember loving just about every second of it. Seeing it again at an older age, it holds up just as well if not better than I remember it. Some Disney films I feel are given too harsh of treatment from critics and I feel should be held in higher regard (The Lion King II: Simba's Pride for example), but if I had to pick the absolute most underrated film (animated or not) to ever come from them, I would have to choose Atlantis: The Lost Empire as one of my top picks.
To begin with, the animation is some of the best I've ever seen from Disney to date. The visuals feel so incredibly huge, they look realistic, they move fluently, the textures are amazingly detailed: One could be completely blown away by this just from the visuals alone. The scenes in the Crystal Chamber, the submarine, the fight/action sequences, they're incredible. The designs are something I can commend too. The look and feel of the city of Atlantis is very creative and awesome to look at, and I always got the sense that this was a real lost, living and breathing culture with a coherent society.
Something I feel this film gets especially right is the characters: Good lord, every single one of them is memorable. Milo, Kida, Sweet, Cookie, Mr. Whitmore, the King, Audrey, I could go on for a while. Each and every one of them have their own personality traits and all have their individual moments, plus no two are alike. Each and every one of them are likable and I found myself satisfied with each and every one of them. The demolition guy I especially enjoyed. Almost every line he said was hilarious, and his personality is hugely enjoyable too.
Speaking of that, that's another thing about this film: Its humor. I can't even begin to count how many moments and lines made me laugh. The writing for the humor is some of the funniest I've seen or heard, and almost every one of the protagonists has a funny line or two at some point. I think the most humorous scene for me were the ones with the demolition guy and Mole. Dear lord are they hysterical both together and on their own.
But on the opposite end of the spectrum, I absolutely love the drama that's conveyed throughout the movie. The story is very well written and it held my attention through to the end. It's definitely one of the most serious animated Disney films to date, and the first of its kind to not have any musical songs. Personally, I loved this touch. While I absolutely adore the songs in many other animated films, here I think it was more appropriate not to have any. The actions scenes are spectacular, especially with the final one that takes place. The violence and the gritty realism of everything makes the physics of its world seem closer to that of the real world (Or live action if you will), and I like things like that in animated films. Many characters die (I won't dare say who or why), a lot of depression sinks in for them, they use real guns, the violence is rather high, and I think it's great. (I'm not one of those people who always drool over action and special effects like with Michael Bay films, but I digress). The physics feel real and nothing is particularly cartoony in it, so I'm very glad Disney knows that kids can still handle serious drama like that.
And one other thing: The musical score by James Newton Howard is absolutely nothing short of fantastic. It could be because I'm a total sucker for chorus and choir music in movies, but the score here felt completely appropriate for the Atlantian setting. It has quite an Indonesian feel to it at times, while at other moments it has more of a Lord of the Rings influence to it, like when there's the loud choir going off in one of the major sequences. Every track has something to it, and it is one of the many Disney soundtracks I dearly wish I could buy to enjoy its full glory.
In conclusion, Atlantis: The Lost Empire is hands down for me the second most underrated animated film to ever come from Walt Disney Animation Studios (Coming in VERY closely behind The Lion King II: Simba's Pride). To reiterate what I said before, I am flabbergasted at the negative critic reviews for it, plus the rating here of 6.7 when that's more than a whole point lower than it should be. Atlantis: The Lost Empire is an absolute gem in the Disney lineup easily comparable to that of The Lion King, Beauty and the Beast, Aladdin, and so forth. It's always one of the first films I think of when I hear someone say they should revive 2D animation for all of these reasons and more.
This truly is a lost classic.