The main changes in Season 2 are the removal of Sudden Death, the addition of Eichenwalde, the new map, and the ratings system overhaul. Most of these will come to no surprise to most players, as all was revealed in a developer update video a few weeks ago. There is also a long list of nerfs and buffs to the different characters, bug fixes and other minor changes.
To start Season 2, players will have to go through 10 new placements matches. Once completed, these matches will determine the player's Skill Rating, which now goes from 0 - 5000, and from there they will be placed in a Ranked Tier.
The new system also determinate who you are able to team up with, if there's more than 1000 points between you and your friends, you are not playing in the same match. For Master players and up, 500 points is the limit. These high ranked players, along with Diamond players, are also barred from playing with those who have not yet completed their placement matches.
Sudden Death is removed, and replaced with a new approach. Depending on how much time the teams had left on the clock, a new match will start with the banked time available. Detailed information on this can be found here. All matches are now a minute shorter than last season, so there's less time to capture and defend too.
If you are interested in reading the Patch Notes in their entirety, they can be found on the official Overwatch forums.
You have until November 17th. Go!
