After the last episode, I certainly wasn't expecting another semi-comedic stand-alone romp. On a certain level, I can see why the writers would go there, but after so many of that kind of episode earlier in the season, I wasn't quite in the mood for another.
Thankfully, this was one of those Trojan Horse episodes that has been a strength of the Supernatural format. Everything about Gary seemed to point towards the case that brought the Winchesters to town, even after Gary set fire to those bones. The truth was a lot more interesting. Tying this to the overall season arc, even in an indirect sense, was a great touch.
In many ways, that redeemed the episode. Sure, it was funny watching Dean react to Gary-Sam, and Sam's approach to family politics tied into the previous episode's point about his anger, without a doubt. But it was also filled with elements that have been done a thousand times before, and often better. The whole mirror routine has gone from being clever and funny to being more than a little self-indulgent.
There were some nice character moments. As much as it made Dean question whether or not "Sam" was himself, there was a part of him that enjoyed the notion of Sam drinking with him. As co-dependent as the Brothers Winchester might be, they are still very isolated within their own worlds. Beyond hunting, they only seem to bond when the situation forces them to do so. That constant state of managed conflict keeps them interesting, but it is part of what keeps them damaged.
Looking at the big picture, it makes sense that the soldiers on either side of the war would want to eliminate the destined vessel for the other side. Frankly, I'm shocked that it hasn't happened earlier. It was getting to the point where one might have assumed that Michael and Lucifer were both demanding that both vessels be left untouched, so that the final battle could progress as planned. Logically, though, one side is going to try to undermine the viability of the other.
It serves to ramp up the stakes a bit more for the rest of the season. Not only do Sam and Dean have to avoid being cornered into playing their destined parts, but they also have to keep foot-soldiers from making a move along the way. All of which may point to one potential direction for a sixth season: even if Michael and Lucifer are defeated, the subsequent power vacuum will leave a lot of chaos to be managed.