There's something nostalgic about running a dungeon based entirely about elementals. Earth, lightening, fire, ice, water, dark and light that both visually and thematically fun. Match this with great rewards and game play could be fun.

I imagine a board with small elemental spirts, medium "titan"s, big dragoons and Gigantic Avatars fun.

Two really great rewards could be increased elemental shards, crystals and clusters for those that HATE gathering and hate the current economic markets for said items.

Another reward is gear with elemental resistance on them. Wearing appropriate elemental armors, weapons, potions, etc could be fun to farm.