There's damage creep and even worse: it's very uneven. Some items got damage boosts and others got very little.
So far, the ADC Mythics feel more like nerfs. Immortal Shieldbow seems to be the preference so far with Kraken Slayer feeling too slow and Galeforce being worthless. Trinity Force seems like a better pick than Galeforce, especially with the crit nerf.
There's also issues with some of the mechanics. Duskblade now grants invisibility without a cool down. This let's Pyke makes multiple kills without being targeted. We also found that there isn't a cap for Armor Pen.
Also, Essence Reaver's Mana return is gone, meaning that ADC's are usually mana starved now. For some of them, this doesn't mean much, but ADC's that rely a bit more on their abilities, it forces them to take Mana flow Band and still be low on mana most of the game. It's a significant decrease in damage.