During Blizzcon, the Heroes of the Storm team revealed that more statistical data would be presented to the players in a forthcoming update. As of yesterday the post-game performance notification system has been released into HotS.
At the conclusion of a match players will be presented with a variety of statistics indluing XP earned, takedowns, objectives taken, etc. Performance is measured through compiled statistics over the course of a week or as long as a month depending on the specific data. This information can be viewed as an individual or vs the community.
You can read more on the Heroes of the Storm site.
