Blizzard has posted a list of the most recent hero balance changes applied to the ongoing Overwatch beta. Several heroes went under the digital developers' knife to improve their overall game play abilities or to reduce overpowered skills.
Bastion, Genji, Hanzo, Junkrat, Mei, Symmetra, Winston, Zarya and Zenyatta all received some attention this week. You can read more about specific changes on the Overwatch forum.