A pretty fun episode with some neat character elements.
I'm not sure if I'd call "Family Appreciation Day" an episode that's often laugh-out-loud funny, but it's one that's very often enjoyable to watch. This comes largely from Granny Smith's consistently entertaining screen presence, which provides a great deal of fun throughout. This is accompanied by character development for Apple Bloom and a few small touches otherwise, and makes for a great episode.
This episode provides something of a miracle: Apple Bloom actually develops as a character. Before now, the character had rapidly stagnated, with episodes she stars in not even ending in a lesson learned like other episodes. Here, she learns to love her family in spite of what bullies say, and that's a lesson worth learning. More than that, it's a start to growth for Apple Bloom's character, and it's indeed the tipping point for the CMC. After this episode, they broke out of stagnation and started justifying themselves as characters.
As said, Granny Smith is highly entertaining on screen. This comes partially from her silly personality quirks, and partially from her enthusiasm and lack of caring for what people say. The former seems to partially stem from Granny going senile, particularly given that she's awfully forgetful, but it's great to see her getting so much out of life in her old age. Granny largely carries the episode, and she's more than enough.
A few small things stand out in this episode. First, the design of the zap apples is fairly neat. The trees contain some sort of thunder magic, and eventually their apples turn a rainbow colour. Aside from continuing the show's slight rainbow motif, this design unsubtly evokes a rainbow after a storm to great effect. Meanwhile, Diamond Tiara seems particularly focused on making Apple Bloom miserable, though her reasoning is even more clouded than ever when her father doesn't seem to be especially abusive or neglectful. This sponsors interest in alternate theories. Silver Spoon, meanwhile, doesn't share Diamond Tiara's sheer vitriol, even clapping at Granny Smith's story, making her easier to distinguish from Tiara.
However, this episode does have some issues. While the magical requirements of zap apple trees are reasonably effective as an allegory for understanding people's actions, they lack much in the way of internal logic, something essential to a cartoon. Meanwhile, a lot of the humour is derived from cringe comedy, and sometimes falls flat because of that. It can be a bit uncomfortable to watch at times, but thankfully some of it is offset by Granny Smith's spirited good nature.
Altogether it's another strong episode, boasting a number of nice touches on top of its strong central characterization. It does have a few flaws, but these are offset by the entertainment value, the character development, and the small window into some side characters' minds. Simply put, it's a typically great episode.