Absolutely gorgeous art throughout. The Dragon Turtle piece is amazing, and I love that they've specified that Gargantuan creatures now have no upper limit on how big they are.
Think they made a really good design decision to incorporate the traditional Lair Action abilities into Legendary actions and then provide additional Legendary Actions and Resistances when you fight the dragon in it's lair. Between that and incorporating different spells for each type, feels like each dragon type will be a much more distinct encounter in 24.
Right away, I am a big fan of making legendary actions unique and not "more of the same attack." It was one of the first things I homebrewed, and I'm sure others did as well in 2014.
I also agree with making humanoids--not. Goblins as fey, kobolds as draconic, etc. It's fresh.