Alchemy balancing
I'm one of the few people who isn't against the idea of Alchemy. I think exploring mechanics that would only be able to exist in a digital space could lead to really exciting and never-before-seen mechanics.
However, I think that taking straight-to-Modern cards like the LOTR set and putting them in with Standard creates a huge power imbalance. Mono-black is dominating the ladder and there's basically no way to beat a Sheoldred/The One Ring combo once its out. The deck carries an absurd amount of removal and redundancy.
We were promised that Alchemy would be a more dynamic format, with balance updates for cards, but since All Will Be One, there have been no such balances.
TL;DR: It's not fun to play against The One Ring, Nazgul, and Orcish Bowmasters in Standard.