I know a lot of people think The Simpsons jumped the shark well before season 12, but I disagree. I still think the show is funny now, and consider that, as high a number as it sounds, the twelfth season was barely past the half-way point for this pop culture juggernaut.
Admittedly, Season 12 doesn't contain any "classic episodes," but it does have a lot of good ones with a lot of very funny moments. I think that Season 12 is a turning point for the show, too. I wouldn't say the show gets dramatically worse, it just changes its feel quite a bit, and it has kept this new feel until the current episodes. The plots are more elaborate and absurd, the guest star cameos feel a lot more gimmicky, and the pop culture references become very current. The humour also gets a little edgier, perhaps due to increased competition from South Park and Family Guy (aka - the worst show ever).
I also want to point out that the packaging for this season is pretty nice, and is completely comic book-themed, from the exterior art to the booklet to the animated menus.
Season 12 starts with a solid Halloween episode, which includes the hilarious Night of the Dolphin short (in which Mayor Quimby delivers one of my favourite all-time Quimby lines: "People, please. We're all frightened and horny").
In fact, Season 12 has a lot of great lines. In the awesome Skinner's Sense of Snow episode, Homer and Ned have this exchange in Ned's car while Homer is driving recklessly:
Homer (singing loudly): I FEEL LIKE MAKING LOVE! FEEL LIKE MAKING LOVE TO YOU!
Ned (nervously): It's a catchy song alright...you really wrote it?
Homer: Yeah. For Princess Di.
I mean, that is comedy gold. It's funny THREE TIMES! It's funny because Feel Like Making Love is a hilarious song for Homer to be singing at the top of his lungs while driving Ned Flanders through a blizzard at top speed. It's funny because Homer told Ned that he wrote it. And it's REALLY funny that Homer says that he wrote it for Princess Di.
The episode Pokey Mom is one of my favourites to catch in reruns. The episode guest stars Michael Keaton as an artistically talented convict that Marge takes a liking to. Other episodes of note this season: Day of the Jackanapes (the Manchurian Candidate-inspired Sideshow Bob epsiode), Worst Episode Ever (Bart and Milhouse take over the comic shop while Comic Shop Guy works on making friends), A Tale of Two Springfields (The town divides in half after a new area code is established, and The Who guest star), HOMR (Homer becomes a genius after a crayon is removed from his brain), Children of a Lesser Clod (Homer starts a daycare and gains a reputation as a perfect father), and Homer Vs. Dignity (Mr Burns starts paying Homer to do increasingly humiliating public stunts).
This season is definitely the dawn of the era where most Simpsons episodes feel more like two or three half-developed episode ideas smashed together into each episode, but that definitely gets worse in later seasons. You can still say "it's the episode where Krusty finds out he has a daughter" instead of "it's the one where a new comic shop opens up in Springfield, and also I think Marge opens a gym or something? And Homer gets plastic surgery?"
It's a good season. It's not season five good, but it's good. Still much funnier than most television comedies. I have really been enjoying watching these episodes again.