I thought it was really good, but the 3 scenes that stood out to me were already mentioned.
The tetris bit complete with music was great.
The Twilight Zone spoof of the mail man breaking his glasses was also great.
And the Marge as Sonny homage to the Godfather part was classic, something I would have expected in season 4.  I actually had to bust out my Godfather DVD and watch that scene again to see how close they were.
Where else can you get a show that incorporates Tetris, Twilight Zone, and The Godfather all in one episode?  And how many people could actually pick up on every reference?  The Simpsons is still teaching us everything we need to know about American culture...