For the record:
Earthworld was based on the classical Zodiac (12 rooms)
Fireworld was based on the Tree of Life from the Caballa (10 rooms, arranged in three intertwining triangles plus one at the bottom)
Waterworld was just 10 rooms lined up vertically with action sequences in the "hallways"
The way objects interacted with the rooms and hallways is different for each game. In Earthworld, the key, Talisman of Passage, and amulet altered the order of rooms and your ability to move through the left and right doors. In Fireworld, several rooms will have doors closed unless you have certain items with you. In Waterworld and Earthworld, you can carry certain items to skip the action sequences. In Fireworld, you can't skip the sequences, but several items will greatly reduce the requirements for passing the sequence.
Overall, Waterworld is the easiest of the three, then Earthworld, then Fireworld. Waterworld only has the action sequences working against you and gives subtle hints as to what items will work for each room's clue. Earthworld has the action sequences working against you and the amulet's room randomizing capability to confuse you. Fireworld simply gets too hard after only a handful of clues as it ramps up the speed of the unskippable action sequences.