"My Sister, My Sitter", written by Dan Greaney and directed by Jim Reardon, stands out as being very dark compared to its contemporaries. The episode as a whole revolves around Lisa's attempt at babysitting, which takes a turn for the worst when babysitting Bart, who refuses to be ordered around by his younger, more responsible sister. Bart's behaviour and Lisa's nightmare-come-true scenario can make "Sitter" an almost distressing watch.
This is the main reason I never used to enjoy "Sitter". In fact, when I was younger I considered it one of my least favourite episodes. As the "responsible" one in my family, "Sitter" rang true with me and I could not help feel sorry for Lisa as she chases Bart and Maggie around, as the situation descends into chaos. What made it worse for me was the fact Lisa had been doing so well before and obviously had tried hard to be a good babysitter, only for Bart to screw things up.
The fact Lisa ends up covered in mud, embarrassed in front of a large crowd of people, with the spotlight on her, made this episode particularly dark for me. I even found that the distressing nature of the episode took away from the humour of potentially funny gags ("and she's on DRUGS!" "Gimme the drugs, Lisa").
Thankfully, after repeated viewings over the years, "Sitter" no longer feels as distressing for me. Whilst I still feel a large amount of empathy for Lisa as she struggles to monitor the chaos unfurling in front of her, I see this as a positive aspect, as relatively few episodes can make me feel so much empathy for a character and still be dramatic and funny. However, the Homer and Marge subplot was largely dull, as it sort of flickered on and off in the episode, before going back to Lisa's story. It failed to go anywhere despite nicely tying together nicely with the main plot. However, there were a couple of good jokes, namely the celebrity restaurant, and, the best joke of the episode:
"This isn't faux dive.... this is a dive"
"You're a long way from home, yuppie boy"
The rest of the humour in "Sitter" is spaced out, seemingly coming in short bursts before disappearing again. The first act proved to be the funniest, with the "Eye on Springfield" segment, and Homer's attempts to lie to Ned:
"Gee.... I'd really love to wanna help you Flanders but... Marge... was taken hostage... in the Holy Land and -"
(I also loved Ned's "anyhoo-diddly-doodle")
As Bart's rampage begins to kick in though, the humour disappears for part of the second act, as Bart starts to test Lisa. I found his behaviour to be mostly unfunny and jerky, although I wouldn't say I hated Bart in this episode, because he did apologise and was needed to create conflict, and I didn't feel it was out of character. As "Sitter"'s second act progresses though, the humour re-appears as numerous people appear through the door, including Krusty, although it's still fairly unfunny. Upon Bart's dislocation of his elbow, the humour disappears once again, as Lisa's struggle intensifies. Here within lies the problem with "Sitter" - for an episode with a particularly dark main plot, the sub plot and main plot just don't have enough humour to balance it out. That said, the episode certainly has it's funny moments as stated. Other humourous moments include: "Oh, loneliness and cheeseburgers are a dangerous mix", and "I like, fell, on a bullet, and it drove itself through me". In fact, Riviera's clinic added some much needed humour to "Sitter"'s main plot, helping it become easier to digest.
Animation-wise, "Sitter" succeeds. Jim Reardon aided the episodes dark theme by making various scenes highly dramatic and compelling. My favourite moments, direction-wise, from this episode were:

I just thought Lisa's stance here perfectly reflected how she was feeling, it's kinda cute too.

During this fantasy sequence (which, visually, was all fabulous), there's some great top down camera angles going on, not to mention some atmospheric lighting and shadows.

And I loved Homer's outfit.
"My Sister, My Sitter" therefore proves itself to be a mixed bag (by classic era standards). Although the episode was well placed, and well directed, with good characterisations, humour-wise, there is perhaps not enough to balance out the particularly dark main plot, which can be seen to be particularly distressing. So whilst on a pure enjoyment level, this doesn't rank highly, I can certainly appreciate its successes in other areas, such as drama, animation, and characterisations.
B
7.5/10
(P.S I'd also like to mention Yeardley Smith and Nancy Cartwright's brilliant voice work here, which I forgot)