Okay, here we go:
This episode had all the makings of an excellent episode, including great characterization, use of new and old secondary characters, and good pacing. I think everyone's pointed out the most obvious bright parts of the episode, so I'd like to draw on what hasn't been mentioned so much.
Pardon my poorly-chronologically ordered review, but I think my favorite part of the episode was the little subplot involving who to blame for Bart's misconduct. Marge feeling sorry for herself and calling herself a bad parent was something I thought would have gone ignored (although in early seasons it wouldn't have, but this shows proof that the show has improved again). The decision to realize the blame on Homer was an even nicer unexpected turn, and for yet another twist, I thought his scheme resolution to compensating for raising Bart badly was the best and most inventive part of the episode. I thought this moment where Homer actually realizes his mistake (not being there for Bart) and trying to fix it by becoming a guard to watch over him was heartwarming and funny at the same time. It was a nice attempt on Homer's part, but as shown, he really is only designated to his shift, and weekdays. A good Homer blunder.
The Itchy & Scratchy cartoon's prison-edit was a great gag too, despite its similarity to the seniors-edit one in "The Old Man and the C Student". It also worked to advance the plot, taking yet another thing away from Bart. I enjoyed Bart's walk through the prison yard, where we really get a feel for his lonesomeness. The slide beatings for one was a comical visual gag in the midst of a more serious scene. The Cletus scene was also great, with the wood-carving psychic being a new aspect to his weirdly hick character.
The Bart/Gina relationship was a different sort of love interest we've seen from Bart in the past, but far more short-lived, and therefore not really my personal focus of the episode. To me, she was there to advance the juvie story more than anything, and the love aspect was just on the side. It was a good way to create a conflict in the episode, where Bart wasn't at fault, and therefore could be excused later and sent back home. The family visiting Gina was just another nice touch to let us feel that Gina isn't completely ignored, since she did help Bart out of jail. I admit this relationship was weak overall, but since it wasn't my focus, it didn't bring the episode down for me. I also thought the Warden was a well-used character, nicely voiced by our friend Charles Napier. Judge Harm wasn't unwanted either. Her explanation for Bart's file was a chuckle.
All in all, I just found it to be a fresh-feeling enjoyable episode with no real cons, and lots of pros. Good stuff, and great addition to the season.
PS: I laughed at Homer's mistaken toilet stall joke. It was all in the delivery.