Ok, so I just finished this thing. Its a great quest Flynn, Southrule was great and this is even better. I like your sense of balance, there wasn't anything too easy in the quest and a few gauntlet like challenges like for the red ring which was very good. Also, powerful items weren't given out too early like the bow and arrow and the wand. And there wasn't any arbitrarily hidden secrets which were mandatory for game progression. Only complaints are that there are peahats which you need to kill before shutters open which can take a very long time depending on how long they hover. And, the magic sword was too well hidden - I couldn't find it but I managed to complete the final dungeon anyway.
Here's my video of me completing your final dungeon: