With regards to the sets: originally sold under the LEGO Technic title as opposed to having its own, the sets were built around certain action-based gimmicks and put a lot of emphasis on the importance of collectible items, like masks. Their gear structures were at times complicated to build, and the figures suffered from limited articulation and very blocky aesthetics. A stark contrast to the later, highly articulated, streamlined and skinny (and at times organic-looking) action figures that came with projectile weapons instead of collectibles, and were easier to build. Many early larger figures initially came in pairs, encouraging kids to duel with them, which can be seen as an extension of the older Competition or CyberSlam LEGO theme. Smaller toys were designed to be able to knock off each other's masks, which was also gradually done away with. The 2015 reboot utilized both projectiles and mask-popping gimmicks in its first year, mostly abandoning them in the second.
Storyline-wise: imaginative setting but a painfully basic, linear plot, focusing mostly on the monster of the year and collecting the current items of importance. No secretive organizations or scheming murderers, barely any sci-fi but a lot of talk about mystical prophecies and legends, and the character personalities are little more than stereotypes. Almost the exact opposite of what it has turned into since the beginning — numerous, decidedly non-straightforward and non-generic plotlines, but in exchange it is very hard to get a sense of atmosphere due to all the differently-toned stories and the constant shifting between settings.
According to a quote from the story writer, this initial weirdness was one of the key reasons why the line didn't receive a movie at its debut. The first year's story was apparently stuck in an indecisive middle-point between the early and bizarre "Doo Heads" concepts and what it eventually settled on.
LEGO itself didn't have normal bricks in green or brown when it started, because even the option to build anything substantial out of camouflage colors was seen as encouraging violence.
The mini-comics included with the first few waves of Masters of the Universe action figures painted a very different mythos than that which would be established later by the DC comic books and the animated series. He-Man didn't have a secret identity and was a Tarzan-esque jungle man rather than the prince of Eternia, and he predominately used his axe in combat - the Power Sword was merely a MacGuffin that could be used to unlock the door of Castle Greyskull. He-Man and Skeletor each owned one half of it, and they were fighting over the complete sword, an idea that was quickly abandoned in later media. It's also worth noting that He-Man (even in the comics, after some of the other more well-known elements were established) spoke in Ye Olde Butcherede Englishe from time to time, of all things. The Castle itself was presented as more of a prize that all the characters wanted to claim for themselves rather than a base of operation for He-Man. Even Skeletor was given a very different origin story - the first mini-comic explicitly states that he comes from a race of skull-faced beings from another dimension and that he wants to conquer Eternia for his people, while every portrayal of the character after the 2002 reboot has used the story that he was originally an ordinary Eternian sorcerer whose face was burned off in an attack with an acid vial Gone Horribly Wrong.
The series bible from the original show includes some ideas that the actual show abandoned and were never used again. Most notably, Snake Mountain was located on another planet rather than on Eternia, and Beastman, Tri-Klops, and Evil-Lyn were all astronauts from Earth.
Similar to the above, the early Beast Wars bonus comics and toy biographies detailed a story that the actual TV show completely abandoned. The characters of Optimus Primal and Megatron were initially described as being new forms of the Generation 1 originals — actually, Primal is the descendant of Optimus Prime, while Megatron simply took up G1 Megatron's name. The story would have taken place in a modern-day setting, and the Beast forms would have came from human laboratories instead of the Transformers' DNA-scanners. The personalities and stats of the characters varied, too — for instance, Tarantulas was at first envisioned as a ninja with an intelligence stat of 4, but the show's writers changed him into a highly intelligent, if very crazy, Mad Scientist. Apart from the story, the first toys also had a bizarre feature called "mutant masks" — basically, every bigger figure had two faces or heads: one robot-face and one based on some kind of animal (not always on the one that the toys actually transformed into). This concept was done away with when the show, due to the limitations of CGI, gave each character only one face.
The original My Little Pony toys were only what are now called "Earth ponies". It wasn't until Year 2 that pegasus, unicorn, and sea-ponies were introduced. Likewise, the ponies were on a sliding scale of anthropomorphic early on (which is why early material has them doing stuff like licking each other and living in stables) but eventually began leaning toward being more humanoid.note "G4" incarnation or not.
The first three generations of Beanie Babies had much plainer designs and no cutesy poems in their tags. Generation 4 introduced the poems or birthdays, and the toys' designs started to become gradually more varied throughout generation 5 onward. It was also at this point that the fad took off in full force.
SH Figuarts in the beginning was very different. The figurines only had the bare minimum of accessories to mess with, usually a couple of hands and a weapon. Compare the original S.H. Figuarts figurine of Kamen Rider Black RX, which only had a few hands, his Revolcane and a ball-joint system which make it look like he was wearing Underwear of Power, to his Renewal version, which not only fixed the ball-joint system to make it more show-accurate, but also gave it multiple hands and the ability to mimic having Black RX pull out Revolcane from his belt. Figuarts from the Pretty Cure series also show the vast difference - compare the sparse options involving the Yes! Pretty Cure 5 GO!GO! characters and the glut with the HeartCatch Pretty Cure! figures.
Epitomized with their Dragon Ball Z line of pose-able figures - the original figures in the line, such as Piccolo, Gohan, and Vegeta had cheaper, looser joints, a flatter paintjob that looked more like clay than actual plastic figures, much more subdued and simplistic expressions, where the grimacing and shouting faces were practically the exact same (if there even were shouting expression faces), and completely different torso to legs articulation, simplistic ball joints with no rotating parts, making any poses besides standing and sitting cross-legged almost impossible. As well, a lot of characters made re-use the original Goku Gi mold or were repaints entirely. Comparatively, the new figures, such as Yamcha, Tien, and the remade Vegeta, are much more expressive, have much better joints, paint jobs that better resemble their manga/anime incarnations and are much more solid and vibrant, and a completely new torso-to-leg joint system that allows much more movement for posing. The older molds are still used, but the figures that use them (such as Ultimate Gohan) usually have a breadth of accessories and are cheaper than the newer mold figures to make up for it, or (in the case of Kaioken Goku) exclusive to events.
The first three dolls of the American Girl line—Samantha, Kirsten, and Molly—were originally released with pale white muslin bodies that sharply contrasted with the head and limbs. To hide this, all their clothing was made high to the throat and with sleeves and skirts (and underpants) long enough to cover this up. This changed in 1991 when Felicity was released; the lower necklines of the Revolutionary/Colonial Period meant that the company could not keep the body covered, so they changed the main cloth body to better match the skin tone of the limbs which is how it's since stayed.