To respond to the steady flood of posts on the Heroes of the Storm Forums complaining of matchmaking problems, Blizzard has made a statement saying they've added a rule to the Quick Match matchmaker to help separate less experience players from seasoned veterans. There are a couple of responses in the thread from the same Blizzard community manager to other questions this has raised. One says they also have some changes in store for ranked Hero League play, but they have nothing to share right now. They also say they are "definitely hearing feedback" about requests for new rules to fine-tune Quick Match team composition based on classes, but they don't sound as concerned about this as they are about experience imbalances: "We're definitely hearing feedback similar to yours, how team compositions in Quick Match need improvement. I don't have any new information to share on this today, though." With apologies to Bill Maher, here's word on the new rule:

To help address this, we’ve created an additional rule for matchmaking in Quick Match that will take each player’s total number of Quick Match games played into account when creating teams. This rule has already been implemented, and we expect that you, your allies, and even your opponents, will now be matched more closely in terms of Quick Match experience.

The new rule will not prevent all instances in which new players can be matched with veterans. As an example, this can still occur when a party’s members have mixed levels of Heroes of the Storm experience. Additionally, this change may result in increased Quick Match queue times as the matchmaker searches for players with a similar number of games played to your own.