Adored by the Network: Along with Persona 3, it's quite obvious that Atlus adores Persona 4, with the two games getting their own spinoff titles and more.
Breakthrough Hit: For the Persona series, up to (and including) Persona 4, the western releases all carried the Shin Megami Tensei name. The success of Persona 4 prompted Atlus USA to drop the SMT branding with Golden and Arena.
Playing Against Type: Johnny Yong Bosch, used to playing the role of The Hero (which he does in this game, seeing as how he's pulling double duty), playing the lovably incompetent detective, Tohru Adachi. Later, it turns out he's playing even further against type when it's revealed that Adachi is, in fact, Ax-Crazy, complete with an Evil Laugh when summoning his Persona.
Tracy Rooney was replaced as Chie by Erin Fitzgerald in The Animation, Golden, and Arena.
Sam Riegel replaced Dave Wittenberg as Teddie in The Animation, Golden, and Arena, as Wittenberg had become part of the voice actor's union since the original game's release.
Kanji is an interesting example - Troy Baker returns in the role for Arena and the first half of The Animation, and his work from the original game is retained in Golden; but Matthew Mercer replaces him in the second half of The Animation and recorded anything that was being added to Golden, due to Troy Baker getting married and taking a temporary leave for a honeymoon.
Naoto's voice actress, who remains unidentified as of this writing, was replaced for The Animation by Mary Elizabeth McGlynn.
Namatame's original voice actor, also unidentified to date, was replaced by Matthew Mercer for The Animation and his new lines in Golden.
Johnny Yong Bosch as the Protagonist/Yu Narukami and Tohru Adachi. More prevalent in The Animation, where Yu actually has dialogue as opposed to the Protagonist remaining silent outside of battle, where his only lines are his grunts and battle cries when summoning his Persona.
Matthew Mercer as Taro Namatame and Kanji Tatsumi, in the second half of The Animation. Subverted with Golden, as whilst Mercer voices any new lines for the two characters, he doesn't voice any of Kanji's dialogue in their scenes together.
There are enough variations of the Valentine's Day scene at school to accommodate the Protagonist dating all of the girls on the Investigation Team. And yes, that also includes all of them.
Events in Marie's Social Link will change depending on when the player does them. More members of the Investigation Team will show up depending on when the player does certain events, and a certain event that lampshades the Limited Wardrobe of rate characters will alter it's dialogue depending on if the characters are in their summer or winter wardrobes.
Similarly, every member of the Investigation Team has a scene in their Social Links where Nanako shows up, usually to cheer them up about something. These scenes will change slightly if you wait until after Nanako's kidnapping.
Rise's original design had her being a playable party member like the others and her being a chain weilding Ice QueenDeliquent. Since Kanji already filled this void, her original characteristic and design ended up going to Ai Eibihara. Speaking of Kanji, he was originally going to be a middle-aged man, and Naoto would've been straight-up male instead of a female cross-dresser. Both of these can be seen in their original concept art.
One of the biggest changes is who the murderer really was… it would have been none other than Dojima, with Adachi serving as the Red Herring instead. It was changed after the ending was shown to a focus group and the feedback was that the twist of the Protagonist living with the killer all year was too dark for the type of game Persona 4 was.
Golden was originally planned to be a PSP title which would've led to features needing to be cut. Thankfully the Vita came along.