I liked Eureka. Just wished crystal farming wasn't such a grind. That's something that puts people off content like Eureka.
I posted a suggestion in the levequest part of the gameplay forum about adding Leves to Eureka esq content that rewards crystals and such.
Maybe add more helpful items like a crystal cluster which lets you respawn without loosing exp. Elemental shield crystals that apply a temporary damage resistance buff.
Add a unique exploration pack where we can keep items and potions relevent to the content so they don't clog up our inventory.
Reduce the mobs needed to spawn fates depending on how many people are in the instance, etc.
Never actually did finish diadem or BA do people still run them?