You know what I hate? They added a "Regional Language" setting, and even if I pick English, most of my teammates talk in foreign languages. They're most likely teammates, but come on, have some sense that the game needs team communication, not a chatroom for 2-3 people. Another thing is that I wish Valve would add that "Ranking" system into full motion. Not because of bragging rights or anything, but for Ranked matchups. I really hate teammates who are really below ranked. Plainly, maybe because of how they play, and it affects the team. Straight to the point, teammates are so stupid. I mean, rarely I have find ever to play with, and also against a team who are evenly matched. Like, there's no bias, and everyone is fairly good or atleast decent in a case. But no, everyone has too be some dunderhead who'll most likely play a carry, or semi, or support that never actually supports, or a ganking team that goes head on so much without thinking, that they would lose.
Valve's matchmaking, might be based on Wins? Or not, maybe just tiering up random people in one match. Wins alone can't determine how good a player is. They should eliminate win counts, loses, abandons, and set up ranks. They should take Starcraft II's ranking system as a prime example of that.
Also...atleast 90% of the players use the All Pick mode. I never got a chance to play on Least Played, to atleast have a fair match.