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.
At least one comedic 4koma series reimagines her as a complete pervert.
Mary probably gets the most of it. Is she genuinely evil and committing unforgivable actions, or is she simply so broken that she's not quite in control of herself?
Garry. A lot of fans like to portray him as a Lolicon with an attraction to Ib, while others insist that his care to Ib is all Big Brother Instinct. The fandom also frequently exaggerates his scaredy-cat tendencies to much higher levels than they were in the game, or alternatively forgets about them completely.
A good chunk of the fanbase seems to theorize that Guertena was evil rather than simply insane.
Even the dolls get this a bit. Some think they are just plain evil, while others see their actions as being protective to Mary, or to each other. Or maybe they really were just wanting to play with Garry and didn't think he would somehow be hurt by their little game.
Creepy Cute: Mary's not the only one who thinks the dolls are cute.
Guide Dang It: Some of the endings can be a little hard to figure out since unless you know the conditions to get them. Also, in the original version, the puzzle where you have to move the stool to the left a few spaces seems to have no in-game hint of how to solve it at all. This one is fixed in 1.04, where there are dots on the floor that indicate where you're supposed to push the stool.
The death of Garry. Though this doesn't have to happen, there is a good chance it will your first play-through.
Even though he's such a minor character, the murder of the painting who helped Ib by telling her the truth was a really upsetting moment that showed just how bad things could get in the gallery.
The endings "Welcome To the World of Guertena" and "A Painting's Demise". Garry becomes incurably insane. When Ib realizes there's nothing she can do to help him, she sinks into despair and never comes out of it. "A Painting's Demise" takes it even further: Mary gives up on Ib and Garry and presses forward alone. After successfully making it to the real world... she learns the hard way that she wasn't meant to leave the painted world, and she dies alone.
Shipping: A large portion of the fandom partakes in this.
OTP: The most popular ships are Ib/Mary and Ib/Garry.
Ib. Gets lost in an art gallery and separated from her parents, finds herself surrounded by dangerous artworks trying to kill her, makes two friends only to lose at least one of them if not both of them to death and/or insanity, is so bothered by the gallery that she constantly hallucinates, and if she gets out at all, it's possible for her to forget everything that happened in there, including the friendship she found in there.
Garry. Gets lost in an art gallery, finds himself surrounded by dangerous artworks trying to kill him, makes two friends only to have to make some really harsh decisions concerning one of them after she goes knife-crazy, runs into trouble with dolls that trap him and try to drive him insane, and it's possible for them to break him completely, he might end up having to trade his rose for Ib's to save her life, which will end up killing him, and if he doesn't get either driven completely insane or killed and is able to escape the gallery with Ib after all, he might forget all about the gallery, including the friendship he found in there.
Mary. A lonely painting who wants to be a real little girl but hasn't been given the love and care that she needs, which has broken her. All she wants is to live in the real world and be friends with Ib. Unless you got "Together, Forever," her hopes and dreams are always dashed. Maybe she became close to Ib only to have Ib sink into despair on her, in which case she either gives up on her dreams for Ib's sake or tries to escape on her own and dies. If that doesn't happen then her desperate actions lead to Garry and Ib distancing themselves from her for safety reasons, and she might end up killed by them at the end.
Woolseyism: vgperson states on her blog that the original title of "Prelude to Wine" was actually..."Grapes." She changed it when she translated the game partly because a nine year old should know what grapes are and partly because it just seemed too obvious a title. "Prelude to Wine" still fits since it sounds more "arty", wine is made from grapes so Garry talking about grapes doesn't seem off despite the title change, and now it makes sense that there's a word Ib doesn't know.