I think Alice's changing size is very interesting. One moment she's too big to fit through a door, and then she shrinks down to a tiny size. It makes for a lot of comical and strange situations, like when she's swimming in her own tears because she's so small. Also, her encounters with the various strange creatures while in these different sizes add to the overall charm of the story.
The trial scene in the story is quite fascinating. The Queen of Hearts is all about sentencing everyone to beheading. There are all these crazy characters in the courtroom, like the witnesses who are not very reliable. Alice starts to grow brave and challenges the absurdity of the whole trial. It shows how Wonderland is a place full of illogical rules and how Alice tries to make sense of it all.