I think there could be an ocean map, where you start on the beach, then the track goes down into the ocean where there are fishes and other sea creatures swimming around. The castle could be a shipwreck. Maybe to do the ocean, have a layer of the top of the sea, then make the track go down underneath that layer
v the layer v
————————/
/. <The track < (it won't be that steep)
/
So track goes underneath the layer of 'water' (it will be different blue blocks probably) and underneath the 'water' is lots of u Dee the sea themed stuff, for example: fish, sharks, anemones, seaweed, crabs, coral and other stuff.
That's my map suggestion :P
As for the current maps, I have played them all and haven't had any issues with them. They're fine in my opinion, but adding the checkered would really help! Thanks for reading :)