The mastery system, a failure by all accounts.

EDIT: Don't just downvote and leave, post as to WHY you think I'm wrong. Enlighten me to how this system has increased player choice, and made more impactful masteries as a whole.

The mastery system in it's current state is just not living up to what anyone wanted.

People wanted to have masteries that MATTERED rather than just small stat buffs all over the place. Keystones are a start, but still fall short and there's MOSTLY stat buffs as well still. Keystones are mostly just on-hit damage/sustain at this point and are all niched into the same use. That's why thunderlords is so popular, it works for everyone.

Riot wanted players to make choices for what to take so that every choice mattered. The new system ends up with LESS choices since you HAVE to get them in certain orders. You can't double up on a row, and thus there's not even as many options as before. You're stuck going fully into one tree all the way, and then going a short way through another. There's no reason to split partway between the trees anymore.

The system REALLY needs to be redone again. Why not have a grid system rather than a tree system, where you can level masteries through your own path? Have the keystones in different directions, so you have to invest a certain way to get them, but the way there is the players choice.

Why not have multiple mastery groups that you can choose from? Have a bunch of small clusters of masteries that are related, and make the player choose which ones then can get.

There's so many better ways to do this than the horrible system that's there now. So many better effects than just +10AD, +15AP, +45health. Higher max CD is great, adaptive armor was one I liked, bond of stone is cool. Why limit it so much with generic +stats.