Riot Games have brought some important tweaks to the experience points system in Patch 13.4, lowering the amount of XP that kills give to champions from level three to level nine.
The balance team explained the intended changes are a way to reduce the snowballing effect that has plagued the first few months of the new League of Legends season. The meta is dominated by strong early-game junglers with great gank setups like Lee Sin, Elise, Maokai, and Jarvan IV, especially at higher Elo (according to U.GG).