Haha, I had the opposite reaction. Dean was definitely more Jensen for me in 410, and I felt it was especially noticeable given that it's one of a two-parter ep. He even looked different, idk. But I actually really dug it. I wouldn't put it down to bad acting either (bias aside =P), not in the sense that he's trying too hard to be something he's not. It felt more natural, and I like to read it as an aspect of Dean that we've not yet seen simply because the circumstances were not right (or bad, as the case may be). I was thinking, wow, Jensen really had to dig into more of his real self for 410, and I dunno, I read it as a mark of deep acting dedication that he was willing to expose (or take a risk, even) more of himself, especially for that last scene. So in a self-reflexive sense of watching, it actually gave the scene more authentic and subsequently emotional impact for me. It also helps that it's a characterisation that is believable given the complexity of Dean's character - by that, I mean that at the very least the possibility for such a facet of his character was there, and it wasn't an adverse 180-degree OOC characterisation.

...um yes, obviously we must talk. =D