Last night's episode was one of the better ones in recent seasons. It wasn't wacky or zany, but rather like the Simpsons episodes of old. It was nice seeing just a little bit of Homer in an episode (and not have the writers call attention to this being a non-Homer-centric episode). I loved the stuff with the satellite dish and when all the TV characters infilitrated Bart's imagination during his test. There was a little too much of Tom Brokaw vomiting, however.
I loved the 3rd grade teacher (I forget her name), especially her hilarious overreliance on the buddy system and her bashing of Mrs. Krabappel and Miss Hoover. And the "Field Trip Wall" outside of the school was a hoot. And I had no problem with Lisa wanting to go back to 2nd grade at the end of the episode; I think this was perfectly in keeping with her character. As another poster said, one of Lisa's character flaws, throughout the run of the series, has been her desire to constantly prove herself more intelligent than her peers. She needs to go back to 2nd grade, so that she could be better than everyone again.
All in all, better than a lot of the episodes we've seen in recent seasons. I'm really glad to see Al Jean is still executive producer. Oh, BTW, "Get Smart" is my favorite TV show, so I just loved the opening sofa gag.
Mike