Oh I can go on and on with specific examples. I love that each subclass has its own feature. I love that so many examples of spells or characters made me - someone who has played over 20 yrs - go "ohhhh, so THAT is how that could look!" (Like Entangle! They made that dumb spell actually cool!) I LOVE that they captured so much description and emotion in just one image. The trickery cleric and the glamour bard and devotion paladin are great examples of this.
My favorite is probably the first page of Chapter 2, how to make a character, that has the characters from the 80s D&D cartoon imagined as actual characters (instead of weird kids). That is an awesome easter egg and I'm surprised no one has made a bigger deal of that yet.
But mostly I LOVE the huge full-page art for each character class!! They're all AMAZING and all of them are like someone said: show me the coolest possible way to represent the true essence of this class. As a sidebar: one of the things I've loved the most about Dungeon World (another TTRPG that has the same "high fantasy" setting as D&D and uses Apocalypse World rules - which are far, far lighter and a much better introduction to role-playing for new players) are the opening paragraphs for each class, which absolutely nail the most passionate, coolest essence of what it's like to play those classes, summed up in a few short words. Those paragraphs alone have blown anything written in any D&D book I've ever read out of the water - by miles. But these images - the ones at the beginning of each class - they are the closest that D&D has ever come to capturing the same amazing feeling of Dungeon World's class descriptions.