The tree of whispers is an OK concept, but it needs a lot of work. The biggest reason by far has to be how unrewarding it is to claim the rewards at the tree of whispers. It gives next to no experience, and most of all opening the caches contains items worse than those that can be found at vendors. The cache honestly feels like a side quest cache in terms of quality.
The cache and bonus experience has to feel more rewarding. Additionally, the item quality needs to go up as the character opening the cache levels up. Being level 90-100 and opening a cache with items all below 725 item power is no fun.