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.
YMMV: American Girls Collection
Awesome Art: The Historical Characters' book illustrations are not only very pretty to look at, but they reflect the time period and setting. For example, the family portraits in Molly's books are in black and white.
The portraits in Kirsten's series are the only ones to have full-body images of the families, and have full background images as well.
Awesome Music: The accompanying background music for the online game "Kirsten's Winter Stars" is absolutely gorgeous. See for yourself: 
The soundtrack to Felicity's movie has some lovely fiddle and whistle tunes as well.
Memetic Mutation: At least some of the characters from the series ended up in a number of Hitler Rants parodies on YouTube. Some of the characters who appeared in the parodies, namely Felicity and Kit, were depicted as way off-character, either ending up being a Screwy Squirrel in the vein of Fegelein, as in the case of Felicity, or ranting like a maniac like Kit and Samantha.
Misaimed Fandom: American Girls Premiere, a computer game released in the late '90s that gave players the ability to write and perform plays about the various historical protagonists and their families and friends. It was supposed to be educational, but it was hard to take the game seriously between the creepy robot voices and the strange movements (characters could even float or walk through walls, and even normal gestures were always exaggerated). As a result, way more people used the game for parodies, Downfallspoofs and poop jokes than for its intended purpose, helped along by the game's almost total lack of a word blacklist.
Narm: Jiggy Nye beating Penny in the Felicity movie.
In the first Addy book, the slave driver makes her eat slugs off the tobacco plants.
In Samantha's movie, a boy working in a factory gets his finger caught in a machine.
The American Girl magazine runs a story contest every year. One year, the winning story was about someone who befriends a mysterious girl down by the lake. At the end, the mysterious girl turns out to be a malevolent ghost. The ghost drowns the main character, who then takes the ghost's place, waiting for the next victim to wander by.
Periphery Demographic: American Girl actually has a lot of fans who are adult women, often doll collectors. They can often be the strictest fans, especially those young women who got into the dolls as kids and apply the Nostalgia Filter.
They Changed It, Now It Sucks: Whoo boy. Mattel took over from Pleasant Company in 1998, and remodeled the dolls and outfits as well as retiring a lot of items. In some corners of fandom, anything made after 1998 is utter crap.
Unfortunate Implications: It's happened a few times, such as the famous incident where Marisol was criticized for moving out of the inner city because it was unsafe and therefore making her old neighbourhood (a real place) look bad. Newsmagazines in 2009 tried to play this up and create a controversy out of minor character Gwen, labelling her "the homeless doll", even though she gets a place to move into partway through the first book she's in, we don't even know she was homeless until The Reveal near the end of said book, and she's not even the main character (that'd be Chrissa).
Addy being Demoted to Extra. She and her items rarely appear in the catalogs, usually with just a picture of her and a note to "find her things at American Girl. com!" Then there are the Fan Dumb who complain about her hair,her skin tone, her accessories, etc.
The Woobie: Nellie O'Malley has a very poor home life compared with Samantha, who also happens to be an orphan.