There are a lot of major changes in this patch that will impact PvP greatly, one being the blanket change to Resilience which now affects all damage taken, rather than just critical hits. Another is the effective neutering of the 2v2 Arena bracket with the change blocking access to the best weapons and end-of-season rewards. A third big change coming is the introduction of a brand new Battleground, the Isle of Conquest, which is the technically the first 40-man raid instance since the original Naxxramas. There's also the whopping introduction of experience gain in Battlegrounds, too. Caught your breath yet? There are a lot of other things in between.