I'll just list the huge changes that affected the game as a whole.
Jungle EXP: the exp of every camp except scuttle crab was lowered to force junglers to fight over crabs in the river instead of just afk farming and picking a lane to snowball. This mostly took any jungler without an early game presence out of the game and now ones like Graves, Kha, and Warwick are seen frequently.
ADC changes: Crit items were changed to be a late game power spike instead of a 2 item power spike meaning that ADC's are extremely weak until they get multiple completed items. This opened up bottom lane to a variety of different strategies making mages and divers a frequent occurrence in bottom lane now.
Enchanter nerfs: The healing and shielding items were all nerfed making supports like Janna and Lulu fall out of meta opening up room for mages like Brand and Veigar and the tank supports like Taric and Alistar.
Ignite buff: Ignite got a massive buff that significantly increased the damage as well as lowered the cooldown. It is now common to have 3 ignites on a team.
