Is there anything Bryan Cranston CAN'T do?
We begin in a movie theater. Homer ticks off Marge by repeatedly yelling jokes (puns, mostly) at the screen. Lenny and Carl are encouraging him, and it's worth emphasizing that their approval means more to Homer than Marge's disapproval.
Then Home gets a concussion at work, and to keep him from suing the nuclear power plant, they give him eight weeks off with pay. (Eight weeks!) As a side effect of his concussion, Homer develops an invisible friend: Stradivarius Cain (voiced by Bryan Cranston), the James Bond-like hero from the movie he and Marge had been watching.
The invisible friend is a staple of shows like this. On American Dad, Stan's invisible friend eggs him into an eating disorder. On Family Guy, Chris's invisible friend pushies him to commit petty larceny. But on The Simpsons, Homer's invisible friend… teaches Homer how to be a better husband.
On first blush, you might wish for Homer's invisible friend to be more "Id-revealing." But think about it: Homer is ALL Id. What hidden urges could he possibly have? He acts on them all! So I think that flipping the usual formula works well here.
(I still don't really understand what Homer actually DID for those two months. But I did love Marge hissing that she knew something was up when Homer left for work on time every day!)
In the B Plot, Bart decides to foil Nelson Muntz's bullying by fattening him up at Krusty Burger. I do kind of feel that making fun of Krusty Burger for being unhealthy is not only unimaginative, it's also a boring re-tread. And it's done within the framing story of a Declan Desmond "Super Size Me" style documentary.
Overall, this episode may have had more in the way of chuckles than actual laughter. But hey, these days I will gladly take a series of chuckles and smiles. Given how tired the "tired" episodes have become, I'm happy for any Simpsons episode that's even remotely watchable. And this one, with its pattering string of silly jokes, puns, and sight gags (like the ad for the "Tic Tac Toe" movie playing in the background at Moe's… surely a commentary on the upcoming release of the "Battleship" movie) is very watchable indeed.