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.
Awesome Music: The music is composed by CÚcile Corbel, giving the film's score a Celtic feel that's both a very pretty listen and unique for a Ghibli production. Arrietty's Song in particular is gorgeous.
Moral Event Horizon: Hara crosses this when she deliberately locks Shawn in his own room, sneakily rather than openly, and with a smirk on her face as she does it for that matter.
Especially with the accompanying Fridge Horror: Shawn has a heart condition and she was warned that even him being startled could set it off. He could have had a medical emergency and been unable to get out of his room to try and get help.
Even worse, merely finding out that the room was locked could have set off his heart condition, as finding that the door is locked and you have no way out of a room is rather scary.
Sho/Shawn. His parents are divorced, his mom isn't around much due to work, and on top of all this he has a heart problem which he is going to have an operation for that he may not survive. You just can't help but feel bad for him.
Also Arrietty herself. She spends much of the film blaming herself for endangering her family, eventually forcing them to move out of their very nice home. Plus in one of Shawn's douchier moments you really empathize with how angry she gets.