Aurum Vale difficulty would be great. I still think it's one of the most challenging dungeons that no other dungeon quite matches. I do think a careful balance must be struck between difficult and tedious: one of the first L60 dungeons, the one with the Gundu? I find that one tedious, but not difficult.

Gooball Library's second boss is especially disappointing because it feels like a complete rehash of an Alexander Gordias boss.

Would welcome more challenging dungeon content, but mind that not everyone wants it to be very challenging and it could lead to abandons from roulettes, the way Steps of Faith continuously invites abandons.