The idea of a spirit who was haunted in life (as the Ghost Host is suggested to have committed suicide) opening up his home to all these other wayward spirits who cannot pass on for some reason and giving them a place to rest and enjoy themselves. He could just as easily have kept to himself.
Since he was such a fan-favorite character, the Imagineers brought back the Hatbox Ghost, with advanced effects that allow him to work! Many fans are overjoyed about his permanent re-addition, and some even claim that he completes the Mansion.
The Ghost Post manages to make one that is also rather creepy. Apparently, all of Constance's husbands still love her, even after she murdered them. And she seems to at least enjoy their company.
The Hatbox Ghost as a character, as in both iterations, his role is that of a justice-seeking Big Good. Originally, the Bride was a villain, and the HBG provides the punchline that connects her to the head-ghosts in the attic's boxes, and in the new version, he hints to the viewers where some evidence of Constance's crimes may be. Even though he's silent, both times his character exists only to expose the Bride in order bring justice to the Mansion and rid it of its only evil.
For all the tragedy and torment that Melanie and her soul has and will experience till Judgement Day, she is still sweet enough, even in death, to ensure that no one will remain trapped within her cursed home like she is as her corpse is seen pointing towards the exit and escape from the Phantom's condemnation...until the 2019 refurbishment removed this, turning Melanie's ultimate fate into an obsessed ghost begging anyone she sees to marry her.
In the film, Emma the maid brings the children cookies, and seems delighted to have someone to dote on. Especially sweet considering that, being a ghost, she can't enjoy them herself, and since Ramsley seems disapproving of the cookies she risked getting in trouble with the big bad just so she could give a treat to their surprise guests.
The film versions' ending, where thanks to the Evers family, all the spirits save Ramsley are freed.
"Angels in Heaven, together at last. The tale is well ended for those who have passed. Love endures all, no reason, no rhyme. It lasts forever and forever all the time."
Gracey giving the family the deed to the mansion before ascending to Heaven with Elizabeth.
"Sell it, keep it, do whatever makes you and your family happy."
Ezra and Emma waving goodbye, hugging all of the Evers one by one.
The fact that they left with Madame Leota and the Singing Heads.
Jim is a genuinely good parent to his kids, particularly Michael who he tries to encourage to get over his phobia of spiders. He's never angry or impatient with either of them; even when he and Megan are trapped in the mausoleum and need Michael to open the door, he stays relatively calm, avoids frightening him and tries to talk him through his fear. Compare this to Megan, who is understandably scared and yelling at Michael to open the door now.
Elizabeth being the ghost ball, especially when you consider that without her intervention, Ramsley's plan would have succeeded. That she indirectly saved Jim's kids from being held hostage tells you enough about what kind of a person it was that Gracey fell in love with.
Disney has released a print, which, in addition to forming a skull shape when viewed from afar, depicts the Hatbox Ghost at the end of his long-awaited journey back to the Mansion, arriving at the famous gates.
In the Haunted Mansion Holiday, Jack brings to the mansion his own brand of Christmas. And the ghosts like it! After what happened the last time he tried making Christmas, it's actually kinda sweet to see that Jack's been able to bring Christmas to someone.
In the video game, after Zeke finds and awakens all the Singing Busts, they sing a song dedicated to him out of thanks.
Singing Busts: "We will speak and we will creak for our meekest brother, Zeke!".