I don't mind the massive continuity errors that this episode introduces to the series. Even though it isn't really "continuity errors" so much as "ripping up the past continuity that has been established over many episodes and crapping on the remains." But you know, it's just a television show. I can let that kind of thing go. I'm sure many fans can't, and will give this episode a thumbs down just on that basis.
"Gone Abie Gone"
Massive continuity errors
But what got me is, this is an entire episode about Grandpa Simpson in which Grandpa Simpson hardly ever appears. Abe is an off-screen character for most of the episode. How can someone be a secondary character in a story arc that is about them? It strikes the wrong note, and made the entire episode feel vaguely "off" to me. We learn much more about the jazz singer Rita LaFleur than we do Abe. I certainly don't feel closer to Abe than I did before.
Another thing that I found vexing was the show's resolute determination not to discuss any of the potential fallout that would have occurred in an interracial relationship in the sixties. (I think the episode is set in the sixties. It's hard to say.)
I think it's safe to say that, depending on when this episode was specifically set, while Abe and Rita were making out in the jazz club, somewhere in America cops were blasting non-violent black protestors with fire hoses and police dogs.
Let me lay some history on you: between 1964 and 1967, many states actually put laws on the books that banned interracial marriage. It wasn't until the 1967 Supreme Court decision in Loving v. Virginia that banning interracial marriage was deemed unconstitutional, and the laws were overturned.
You may think "Well, that's a pretty heavy burden to put on an animated sitcom." But I see this kind of thing often: the whitewashing of American history. And I refuse to accept it.
Whitewashing history does us all a disservice. Both the people watching the show now (who may or may not be aware of how hard it was to be a black person in the 1960s) and the people in the 60s who fought for change. It's not right to pretend like an interracial relationship would have been fine and unremarkable then, and frankly I expect better from The Simpsons. Maybe I shouldn't.
Oh, and also there was a sub-plot where Homer stored Lisa's college money at an online poker website, with predictable results. The end.