These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Base Breaker: Sid and Shira, given the responses to them from the fanbase. In some cases, they are either totally loved or sincerely disliked. (Mainly because of the writing decisions taken that involved them.)
Contested Sequel: All of them, espicially the third, which is quite contested, some consider it an absolute disaster, others call it the best of the trilogy. They are contested especially by those who can pretty much see past Fox's intentions of trying to create a Cash Cow Franchise to match with that of DreamWorks' Shrek; Continental Drift seems to be forgivable with some, if only because of Wanda Sykes as Sid's granny.
Crack Pairing: Many, but notable ones include Sid and Ellie/Sillie and OT3s like Manny/Ellie/Diego. Supreme crack pairings include Peaches x anyone, but these have been mainly only discussed, though Sillie has been written once.
Rudy/Buck is another example. Sid/Diego probably counts as well, since there is really no viable reason to pair Diego and Sid together, let's be honest, it's Pair the Spares if anything else.
Creator's Pet: Both Scrat and Sid both show shades of this, Scrat since the first movie and Sid was Creator's Pet primarily in Ice Age: Dawn of the Dinosaurs. Because of this, the two have divided the base between fans, some disliking Scrat as being a nuisance (which he is) and Sid as The Scrappy as Flanderisation has ruined his character in between the Original film and its first sequel, The Meltdown and Dawn of the Dinosaurs. ..... oh, and Scrat is voiced by Blue Sky Studios director/producer/founder Chris Wedge. Make of that what you will.
Draco in Leather Pants: Some fans like to over-romanticize Soto as this. One person to such an extent that the Sub-Zero Heroes become Ron The Death Eaters, Diego especially, because of the whole "brother with Soto" fanon.
Louis the molehog from the 4th movie. He just oozes Moe.
Gutt's crew also got their share of fans, particularly Flynn.
Fanon: Manny's first mate and child's names being Millie and Wally, due to one author on fanfiction.net creating a ripple effect with the names.
A lot of fans like to think that Diego and Soto are brothers. But this interpretation turns sour when you realize that in the entirety of the Original, Soto is subtly making plans to kill Diego himself. What his DILPing fans conveniently don't notice is that it leads to a Cain and Abel motif in the first movie if you subscribe to this fan theory. The Original film displays this trope terrifyingly if this fanon is "true", as every move Soto makes towards Diego is to devise the death of his own brother. Thus making it even MORE Darker and Edgier for the first installment.
Another new, disturbing fanon beginning to crop up is that Soto is Diego's father. Given that the Original implies that Soto is slyly setting up Diego for his own death (one reason why some people don't like viewing the two as biological brothers) fans joining together under this fanon is a whole new level of Do Not Want.
Also, Soto being Not Quite Dead pops up somewhat commonly in fanfiction.
It's also become extremely common to see fanfic writers have Diego and Shira use the terms “Kitty” and “Softy”, respectively, as pet names for each other.
The implication that Runar's tribe killed Manny's family. It's never truly established as being this in the film, but fan reading of canon often goes with this conclusion.
The implication that the two rhinos at the beginning of the Original film, are a gay couple. Blue Sky has given no official confirmation for this, but most fans (casual and hardcore) tend to read them as a couple, but it's still fanon. And oddly enough the world of Ice Age fanfic ignores them as well, when the fanfiction realm is well-known for its love of slash pairings. Make of that what you will.
A popular fanon after Dawn of the Dinosaurs' release was that Diego was having heart problems. Despite this being Jossed in the director's commentary with the confession that Diego was out of shape, there were still several fanfics written based around the inaccurate fanon, with some fics using it as an excuse to kill off Diego because he was "getting old" even though that, like the inaccurate heart problems fanon, was Jossed by the creators.
Fan Preferred Pairing: Peaches/Ethan has become this, despite Peaches seeing Ethan as shallow in the fourth film and going off with Louis at the end. Also, Sid/Diego has long been this for some time in the fandom, despite the pairing being nothing more than a Crack Pairing and Pairthe Spares.
Germans Love David Hasselhoff: The Ice Age films have all had decent box office runs in North America, but, at least in the case of the sequels, were overshadowed by the films from Pixar and Dreamworks Animation. Overseas, the series has been very successful, withallfourfilms in the series being the highest grossing animated films worldwide in the years in which they were released.
The movies, especially the first one, are really popular in Norway. One reason in particular being famous comedian with Bergen accent Dagfinn Lyngbø voicing Sid, who've more than once been recognized as making Sid several times funnier than the original.
Genius Bonus: Buck's attitude and tendency to fight Rudy is very akin to real weasels, which are known to be fearless and attack prey bigger than themselves.
Harsher in Hindsight: Before the heroes enter the ice cave in the first film, Sid is joking around by pretending to be impaled in the neck with an icicle. How does Soto die again?
Hilarious in Hindsight: In 2002, there were no known mammals extinct or extant that closely resembled Scrat. Come late 2011, one was described and named Cronopio. (However, it was not a squirrel, but part of a now-extinct mammal group, the dryolestoids. Furthermore, it lived in the Mesozoic Era, not the Cenozoic as most of the other animals in the films are.)
The presence of Buck in the third movie can be this once you discover that 20th Century Fox had once planned to adapt The Wainscott Weasel, a children's novel whose main character is also a weasel with an eyepatch.
Also in the fourth movie, we have Manny trying to break the sirens' trance by singing "The Candyman", which happened in the Dreamworks movie Madagascar. This would later head in the opposite direction, with the Running Gag of the rabbit on Gutt's crew being called the Easter Bunny... which would become a thing in Dreamworks' Rise of the Guardians.
Moral Event Horizon: Captain Gutt crosses it by trying to kill Manny's family in cold blood just to get back at him.
Soto crosses it early on in the first movie when he talks to Diego about his plans for revenge against the humans: kidnapping the tribe's baby and then eating it alive.
Pair the Spares: A very likely explanation for why Sid/Diego is so popular. It requires little thought and is really only pairing the two spares.
Periphery Demographic: Though the films are ostensibly aimed at younger audiences, the movies - for example, the first one - have attracted a lot of teen and adult fans, who enjoy the Original for its depth, humour, dramadic elements, and tearjerking moments. The sequels have admirably brought in teen and adult fans as well, and one reason the movies have such a demographic is because young fans of the Original realised that the sequels kept up with the Original in some regards (ie emotional plots and captivating characters), since some of the teen/adult audience watch the sequels in hopes of seeing characters like Roshan again or just revisiting their old friends the herd.
Shira + Diego = Shego, though the pairing is more commonly known on ff.net as "Dira."
Rewatch Bonus: Soto's hostility towards Diego and his subtlety in threatening him are often lost on some viewers of the film. However, if you go back and watch it again and notice every single Implied Death Threat and Soto's constant allusions that put Diego out of the picture with the pack, it gives one a very different view of Soto and how he really feels about Diego.
The Scrappy: Sid is sometimes regarded as this by fans who aren't as fond of him as they are of Manny and Diego.
While Sid and Scrat have their faults, they at least contribute to the plot and give a few laughs. Crash and Eddie don't. Those Two Guys are annoying, and if you remove them from the third and fourth film, the story will be completely the same. Even in the second they are not very useful, as all they do is making Ellie, a mammoth, believe she's a possum (whether because they are stupid, or because they want to keep her as a sister, which is no better). They are reduced to background characters in the fourth film, and appear only to give some gags. And they can't even do THAT right!
Shira from the fourth movie, much like Lola Bunny, is a boring "tough girl" clone of one of the main characters who only exists to serve as a love interest. Not only that, her pretty white fur and flawless face sticks out like a sore thumb amongst the more ugly pirates, with the only part of her that's even remotely asymmetric being that she only has earrings on one ear.
Teenaged Peaches in the 4th movie also gets this for her plot of that movie being pretty much a cut and paste of a million teen sitcom cliches.
Strangled Bythe Red String: One could argue that Diego and Shira's romance in the fourth film was this because it wasn't built up much, happens way too quickly, and unlike Mellie, they do not share any intimate emotional scenes that could grow Shira (or Diego) as characters through their romance but instead spend most of the time snapping at each other until Shira randomly decides to side with the herd. Heck, Shira remains an entirely one-dimensional Love Interest throughout the film, something that sticks out like a sore thumb when one compares how well Ellie was written in The Meltdown.
It should also be noted that Ice Age got an Oscar nomination for Best Animated Feature Film the year it released, thus the CGI in the first film couldn't have been that bad if the Academy approved of the work seen on the film.
Unintentionally Sympathetic: Soto tends to come off as this, as people feel sorry for him that he lost his pack/family, and was probably a pretty amiable guy once, and some people ignore his bitter desire for vengeance against the humans as it detracts from him being Unintentionally Sympathetic.
Viewer Gender Confusion: Roger, Buck's pterosaur mount, is referred to as female in the video game version of Ice Age 3.
What Do You Mean, It's Not Symbolic?: Manny rescuing Diego from the fiery flames of the lava. Not to mention that Roshan's role in the film is a "Peace Child" between the humans and the animals, and it's his innocence that helps redeem Diego, helps Sid find a new family, and gives Manny closure after his family's death, and reconciliation with the people who destroyed his life. It's one aspect of the Original movie - that is, Roshan's importance - that is often glossed over, but he changed all of the characters taking care of him because of his love and innocence, was central to character and plot resolutions and by the end Manny, Diego and Sid are a herd because of Roshan bringing them together as true friends.
The ark in The Meltdown.
Also Scrat falling off and "dying" after saving everyone.