There's a reason why characters appear different in several panels — they are being seen through other characters' eyes, which is more prominent with how the protagonist Taichi is drawn. While the plot takes place mostly from his POV, he is drawn very simple, clearly awkward and somewhat goofy, but when it's clear that the focus changed to another person, he is drawn differently and often more handsome because those characters are in love with him and see him as more handsome than he sees himself. This is most notice when Futaba and Toma are the POV characters.
Similarly, the constant appearance of characters in a more caricatured style makes the scenes where they are serious and drawn in a more detailed manner all the more impactful, as well as the comical scenes even funnier.
The characterization of Mami. In-Universe, people are suspicious of her motives before really learning about her. It is also an intended reaction for the readers as when she is introduced, they thought she might be two-dimensional and would hurt anyone who gets in the way, before her chapters came and we see a lot of baggage that Mami is carrying due to those assumptions.
The series ends on a shot of Shibuya. was one of the first areas in Japan to recognize same-sex marriage by granting official certificates and is almost certainly where Toma and Taichi got married.
