Basically there are now two big buttons on the front screen. Hiding behind the "Arcade" button is a list of custom game modes that lets users quickly rate and find specific custom matches with a rotating carousel of choices always on offer. The "StarCraft 2" button hides all of the traditional multiplayer stuff, the single-player campaign, leaderboards and the like.
The other big addition in this update is a new pipeline for speedy patching. This new data streamer will allow the game to download patch data during play, which Blizzard hopes will expedite wait times in the future. The full patch notes can be found through the source link below.