Generally quite simple in terms of scripting, a few remarks:

• There is no "you lose" opcode, instead it simply loops back to the intro screen
• Some rooms are empty and unused (maybe there was more to it but it was simplified a bit)
• One single variable is used, 8-bit variable 01, to indicate if you have found the key: set when you find the key, clear when you die (since this does not "properly" reset the game), and tested when you need the key.
• Only a few rooms use multiple screens, and not very consistently. In some cases, there are long successions of different rooms that could just be screens (not that it really matters, unless you're trying to find your way in the 80-something rooms in the debugger).