LP Gainage/Loss
One of the most discouraging things in League of Legends is the amount of League Points players earn after a ranked game. When someone queues up for a ranked 5vs5 game, their incentive is often the hope they'll earn LP, climb the ranks, etc. When you give it your all that game, someone feeds, someone throws, whatever; if you come out with a loss, you're likely to be devastated. Other than IP, which is virtually useless once all the champions are unlocked, you're not being rewarded for a loss, which makes sense, to an extent. Not only are you not rewarded for finishing a game, but you're actually punished significantly harder for losing a game than you'd be rewarded for winning one. For example, I just won two games in a row, 18 LP each, a total of +36 LP, but then I lose my next game and lose more than half my winnings: not very balanced, and quite frankly tedious for players that stride to get better at League of Legends.
All in all, what I'm trying to say is that the LP Gainage and Loss is not equal, and discourages players from losing, which creates a very toxic environment for players, particularly those whom take the game more seriously than your average Summoner.
I call for change, hopefully in preseason.