I'm certainly not an expert, but I'll pretend to be. I saw Dustin Hoffman in Death of a Salesman at Lincoln Center and hated it (I know, call me a philistine). All I could see was D-U-S-T-I-N H-O-F-F-M-A-N playing Willy Loman. I had a similar reaction to Jensen in season 10, especially and somewhat in season 9. It's just too loud and over the top for me without much modulation. Maybe it's the writing and direction that are the problem ::cough cough hacks cough cough:: although I can't really tease that out.
So far this season, Dean is showing very, very little emotion which also is driving me crazy, because I want to know what the hell's going on with Amara. The show is usually exposition heavy, but here's a storyline that could really use it. IMHO