Great episode! As far as "modern era" episodes go, The Ziff Who Came to Dinner was nearly perfect. Let's start with the couch gag: this is without a doubt the strangest couch gag ever, but it was quite a cool one! And it's nice to see a chalkboard gag after quite a long string without any.
On to the first act: there was one fundamental problem with this act. It had nothing to do with the rest of the episode, and was a waste of screen time. However, it was an absolutely hilarious waste of screen time! Nice to see a return of the parody movie titles ("A Matrix Christmas"), and good characterization of Bart and Lisa. Lisa trying to rationalize her fear ("It's just a movie, filmed in Vancouver") and failing struck me as great interpretation of Lisa's character: incredibly smart, but still an eight-year-old girl. With some similar Bart scenes, this was some of the best characterization we've seen of them in years.
The second act, while forgetting about every plot point of the first act, still worked very well. Artie's explanation of his downfall incorporated a very small but funny bit of social satire (Gingrich, Garofalo, and Pippin in the hot tub, claiming that the stock "will make a slight rebound in 2003"). Artie moving in with the Simpsons felt slightly forced, but not nearly as bad as earlier similar incidents (the convict in Pokey Mom immediately comes to mind). Artie framing Homer, on the other hand, felt completely within Artie's character. Even with the questionable concept of how Homer got the stocks, this part felt perfectly natural. A couple more notes about this act: I liked the meta-reference of John Lovitz's previous characters. A nice injoke for knowledgable fans. Also, Barney was drunk again? Woohoo! It's about damn time!
Act three opened with a very good thing and a very bad thing. The good: Krusty sitting on the Congress committee was a nice bit of continuity. The bad: in this scene, Homer acted much, much dumber than usual, which is a real accomplishment for him. Oh well... it was only one scene and didn't really hurt the flow of the episode. I loved Artie's daydream in the courtroom scene; it was kind of reminiscent of the classic "I am evil Homer" daydream from Whacking Day. The scene with Homer in jail was sufficiently touching, which still maintaining the feel of the episode. Patty and Selma's entrance into the episode was kind of strange, but worked well enough. Selma's attraction to the man who put Homer in jail made some sense. Artie's decision to come forward may have happened a little too easily, but the writers did a good enough job establishing the reasons for this. The ending, with Artie in prison, was funny, and did a good job of providing closure to the episode.
Overall, The Ziff Who Came to Dinner had a couple of minor problems, but were overshadowed by the good plot, great characterization, and fantastic humor.
An easy 4.5/5!
My score: 4.5/5