I have to hard disagree here. Advantage/disadvantage is the single best innovation in 5e, IMO. It speeds the game up immensely, is instantly understandable, keeps the focus on consequential dice rolls, which is just fun, and provides meaningful consequences without adding extra math. It definitely improves my games. A lot.
Edit: but then, I'm generally anti-modifiers. 3e, for example, was very problematic for me in how many modifiers you had to track and stack, and at higher levels modifiers easily outweighed the dice rolls a lot of the time. Advantage/disadvantage, combined with bounded accuracy, is so much more elegant to run. I have a lot of players with math challenges, and I don't think I could get nearly the uptake if I presented them with a system like 3e.