1) The variance in how much rating you lose/gain is just much too wild. One game the bar goes up/down barely an inch and the next it's "WOO IMA GONNA MOVE AN ENTIRE FUCKING RATINGS WORTH OF BAR!". Even taking MMR differences and "performance" into account, that's just weird.
2) I'm still not sure that ratings mean much right now. You still find extremely mediocre people at high ranks and suspiciously well-organized people at low ranks. That's not to say that "organizing" certain things is hard or anything, but when the enemy Zarya throws up a barrier on Reaper right as he runs in and pops Death Blossom, then she lobs her Gravity Well right at all the people who ran from the Death Blossom and right at that instant the Hanzo dragon flies into all of them...ok, that's not "Rank 28 PUGs" organization there, something else is up.
Meanwhile a friend of mine is Rank 74 and he still rages because his teammates run off the map, or one of them is a "Bastion Main", or the Soldier/McCree on the team can't hit the enemy Pharah to save their life. So on and so forth.