“Mother Simpson” is an excellent episode for any number of reasons, primarily because it is terribly funny.  But considering it in the context of the writhing horror show that is Zombie Simpsons there are two salient points:

• The first is that it has an ending (pictured above).  Despite its many plot twists* there’s a reason Wiggum calls the Simpsons to warn them.  It doesn’t just happen apropos of nothing as so many Zombie Simpsons endings do.
• Second, it doesn’t draw out its suspenseful/emotional moments.  When Bart and Lisa figure out that Grandma’s story is fishy there’s no montage of them spying on her in wacky ways.  When Homer and his mom share an “Awwww” type moment there’s no extended use of the string music of sadness.  When Burns & Co. find out who she is there isn’t a drawn out chase scene.

*They still had the good sense to make fun of themselves for all the drama with the Dickens/Melrose Place line.