Hilarious in Hindsight: The story of Effrafax of Wug's bet to make a mountain disappear and how he would have succeeded had he merely painted the mountain pink and erected a Somebody Else's Problem Field on it. A few books later and Douglas Adams would be writing about an Electric Monk who believes his world to be... pink.
Nightmare Fuel: The Krikkiters, who only want to, you know, kill everything that isn't Krikkiter.
So Okay, It's Average: Generally agreed to be this in relation to the other books. While definitely not as fondly remembered as the first two books, it's certainly better remembered and more highly regarded than the two books that followed.