patch 1.0.5 adds the Monster Power system, which allows players to adjust the difficulty of enemies in Normal, Nightmare, Hell and Inferno modes, along with a lengthy change list affecting the Auction House, Battle.net, Bosses and Classes, among other aspects. Blizzard began launching the patch today, October 16, and the game will be under scheduled maintenance at staggered times in each region.
Maintenance for the Americas began at 3 a.m. PT and will conclude at 1 p.m. PT. Europe's maintenance begins at 6 p.m. PT and concludes at 4 a.m. tomorrow, October 17. Asia will be under maintenance from 1 p.m. PT on October 17 to 11 p.m. PT that same day.
Check out the entire change list here