Man, this episode seemed really pointless. I know it's a parodyistic coy version of "Inception" with bed-wetting and I've seen inception, but this episode seemed like it was nudging you with "look, it's an Inception parody, huh, HUH!? Laugh, damnit!". Yeah, the Ullman short and Mona back for a moment was nice nostalgia, but this episode was too "it just happened for no reason" for my tastes--Frink just happens to land in front of Marge...Wiggum just happens to show up at the Simpson house, etc, and I know it's a cartoon so STFU.
Anyway, it was either too stupid, or it was actually funny, like when the crowd was throwing crap at the family in Lisa's dream, or Moe being used to slow up the gears, but Bart dancing in mid-air, ugh, or the urine alarm (it would've been funnier if Homer wet the sensor pad and got an electric shock for some negative reinforcement).
So, with the good and the bad, it comes out an average 3/5 for Zombie Simpsons, yes, I said ZOMBIE SIMPSONS and if you don't like it, don't go to bed angry and piss on your sheets!!!
EDIT: When, not if, a full-fledged SimpsonLand opens, you can bet the Homer-Coaster will look just like this on in the post above.