Where do you want to start? The player mechanics are way outdated and overcomplicated for what it wants to be, the GM mechanics are functionally nonexistant, the lore is cliched at best and still incredibly bigoted in many areas, the better adventures are just rehashes of 2e and 3.x adventures and still need entire communities dedicated to making them runnable, it’s unbalanced until you get to about level 10 at which point it becomes unplayable, and without pirating it’s incredibly expensive.
Trying to strap every possible setting and mechanic onto a fantasy rule system was one of the issues 3.x ended up with, and 5e hasn’t been designed to solve that.