I totally agree. Ovechkin, for all his talent, is a dirty hockey player. He frequently launches himself at other players, leaving his feet to body check opponents. On the play in question, his two-handed slash was egrigious and more worthy of 5 and a game than Niskanen. As unfortunate as Niskanen's play was, I aceept that he was 'defending himself' - it was not a high stick - Crosby was already going down when contact was made, well below Niskanen's shoulders. There was little, if any forward cross-check motion. 
Hopefully Crosby is ok and not overly concussed. Given his history, it's not good.
And yes, Crosby should have had discipline himself for the Methot incident. I agree that the hard slashes disguised as stick checks are very dangerous, as whatever is left of Methot's pinky will attest.