Thanks for this very nice comment.
The transition animations are pretty simple actually, each exit is an Area2D with a two collision bodies (one for each side) this ensures that I can detect the player going in from the left and from the right. Within the body is a sprite. The sprite is constantly rotated and its scale is enlarged, if the player has entered the door.
I use the onready function to do the opposite of the transitions, so that the door animation plays to swoosh the player into the next room, and also swooshed to de-transition :)
I can share the code if you like but I think the general idea is enough to get an understanding of the principles, so that you may implement it into your game :)
Good luck
