I like how the humour isn't just the random bits from the trailer like in lower-quality animation films (like some Illumination ones...). It is actually really funny for at least the whole first half of it.

But what makes it one of my favourite films is the emotional layer of it. It depicts anxiety in a very relatable and probably accurate way, which also resulted in the film claiming the spot of the film that made me cry the most haha. The relatability and compelling-ness of the emotional layer depends on your personal experience, probably, but I still think they nailed it.