After the disastrous events of the previous episode (and a nice-sized winter hiatus), I wouldn't have blamed the writers for dialing things back a bit. Not back to the overabundance of comedic episodes that marred the first half of the season, but some measure of respite would have been understandable. Thankfully, the writers went with something with more punch than punchline.
I've said it many times: the strength of Supernatural is the attention spent on character psychology. The writers understand that character is king, and that characters can be complicated under stress. Some may call this the "emo"approach, but I think it's the smart approach. Tailor the plot to serve the purpose of exploring the characters, and in many respects, the characters will tell you where the story is going to go.
Under their current circumstances, the Brothers Winchester have to be honest with themselves about their weaknesses. Michael and Lucifer want to use them to carry out their grand conflict, in accordance with God's apparent plan, and both sides are going to try to force the issue by preying on Sam and Dean's vulnerabilities. Unfortunately, especially in Dean's case, the brothers have a bit of a problem communicating on that level.
In this case, it's not about presenting a strong macho front. The best offense is a good defense. Whatever avoidance tactics are needed will depend on where and how they think the enemy will come at them. Dean needs to see that his exhaustion and growing hopelessness, never mind his guilt complex, is eventually going to tear him apart. As his hallucinatory hot doctor said, there's only so long that a person can drive themselves at such a harrowing pace with such an impossible goal. The burden is just too much to handle. If Dean ever gives in, it will be because he just can't fight anymore.
Sam, on the other hand, is driven by rage and resentment. His guilt is largely a symptom of rage towards himself, at his inability to prevent his own weakness. It's the kind of anger that has the potential to get out of control and overwhelm his judgment. And for better or worse, Sam's ability to resist Lucifer is absolutely dependent on his ability to control his emotions. If Sam is pushed hard enough, to the point where he is no longer rational, then he could offer himself to Lucifer in a fit of nihilistic rage.
I also like the fact that the writers are not letting Sam off the hook in terms of Ruby and his choices in the fourth season. Ruby may have been one hell of a manipulater, pushing all of Sam's buttons, but on a fundamental level, Sam knew what he was doing. Demon blood may be addictive, which made it easier for Sam to be influenced, but Sam was still responsible for his own actions. Tying that into his anger is a nice touch.
The setting of the episode was perfectly designed to explore all of these issues. The Wraith was an interesting creature on its own, with a requisitely nasty way of dispatching its victims. It was a nice comedic touch for Sam and Dean to use their actual life as a basis for their "delusions", and it was even better that the Wraith pointed out how it completely undermined their mission! (And the ladies of the psych ward, delusions and Wraith-disguises included, were gorgeous!)
Perhaps the best aspect of the episode was the very end. To a certain extent, it could have been interpreted as a resolution of sorts. But in the end, it's really just an acknowledgment that they have issues, and they just don't know how to resolve them without losing it. Dean's solution to Sam's anger management issues is essentially his own psychosis! After all, the point of Dean's subplot was to highlight how his inability to manage the extent of his burdens is slowly destroying him!
And because we know that Dean isn't going to fix his problem, and we know that Dean's approach only delays the inevitable, we also know that it's just throwing a bandage over Sam's issues. In other words, the end effect of the episode is to show the audience how the Brothers Winchester are most vulnerable, and that they have no idea how to fix it. And that is quite a nasty bit of foreshadowing.
And that makes sense. This is the mid-point of the season, so the writers are knee-deep in the complication phase. If the Brothers Winchester are going to get their act together, it's not going to happen for quite some time. There's still a long way to go before the end of the season.