First absolutely standout episode of the season for me. That was really, really, really, really, really, really... good.
The episode did really look beautiful, I'll give them that. I've been loving these past few episodes and their use of snow, even when a story doesn't necessarily call for it (though this one did). Just, everything was really gorgeous, the characters all looked great, and Charlie actually had an absolutely fantastic design that allowed him to blend in with the rest of the characters seamlessly. So just watching this alone was a pleasure.
But even better - it had not only a well thought-out beginning, but even a well thought-out, not out-of-nowhere end. The entire story felt developed and fleshed out to as great an extent as was possible for the limited time, and not once did I feel really taken out of the plot due to this, and I was never really questioning any character's emotions or decisions or anything. Things were actually genuine here and while being Bart-centric, the whole family was well-included and all were relevant to the story; no gratuitous appearances.
Lisa and Maggie's bonding was cute, and Lisa's teasing of Bart rang true for a sibling relationship. Bart's interactions with Homer showed exactly the kind of relationship I like to see between the two. Homer isn't borderline retarded, still actually does care about his son, but is somewhat realistic about it. Bart goes to desperate measures, Marge catches him in the act, and they have a genuine heart-to-heart as well, like the two have shown in the past (and this episode wasn't even a focus between the two).
Not to say this episode wasn't funny, either, because it certainly did. I was wondering what Bart was doing wearing a Stan-like hat, since that would have been a weird coincidence (and considering how this is animation and it was specifically drawn that way, not really much of one at all), but then the South Park parody was... absolutely fantastic. Hilarious and perfectly played and I really was not expecting that. Likewise, the Sex and the City parody worked as well. It wasn't forced, it came naturally, it was relevant to the plot, and... just great. (Plus, I really would imagine that having three sisters like that would be a horrible fate - poor, poor Charlie. Kid may have maced Wiggum, but he sure didn't deserve that.)
So yeah. This episode actually made pretty good use of the four act format, finally. Bart comes to understand he wants a brother, Bart tries to get a brother, Bart does get a brother, and brother has to go away. Clean cut, smooth, nothing forced, and completely enjoyable.
It really does help here that Bart is my absolutely favourite character and he was in top form this episode, but without even considering that - everything had a natural flow. The episode looked beautiful. It was funny. The dream sequence was fantastic. Bart and Charlie hanging out together was great. Many episodes have had a well-developed beginning; this one had a great end - not quite as well-developed, but hardly out of nowhere, either.
It was satisfying, entertaining, best of the season thus far, really standout in this recent era. I'd actually love to rewatch this one.