As far as I am concerned the only thing that 5e did that had value was introduce Lair Actions and Legendary Actions.
Advantage/Disadvantage is a TERRIBLE mechanic.
It reduces everything to the same roll and removes all reasons for the PCs to work together to find synergies with other characters. It makes every advantage basically and auto hit and makes any disadvantage an auto miss.
5e coddles to the "All Children Left Behind" generation who can't do math. Do you know how hard for a PC to die? Three Death Saves? Pfft, here, have a participation trophy with that.
Woke DnD? Racial Attribute modifiers are racist? So it is racist for Elves to have a high DEX and Dwarves to have a high CON? Really? is that what DnD has been reduced to? LMAO.