My older sister and brother are Gordon Korman fans. They love his early, zany books like the Macdonald Hall series, Losing Joe's Place, and Don't Care High, while ignoring (most) of his newer stuff. D (the sister) mentioned that the most recent Korman book that she read, Schooled, was good, but not a "pure" comedy, which Korman excelled at while in high school.
Well, duh. I read and finished the book last night, and it was EXCELLENT because it was about a homeschooled idealist kid who becomes president of the local middle school after his teacher (aka grandmother) breaks her hip. The ending seemed pasted on, but it was a great book because Cap, the idealist kid in question, never breaks, to the annoyance of the local school bullies. And yes, it had serious stuff, but the serious stuff made the book even better.
In general, I prefer a mix of comedy and drama in my stories because the complementary tones each help the other from going over the top. To do a pure comedy, like Little Miss Sunshine or Don't Care High, is difficult because you have to make the comedy the dominant form. And since not all humor is universal (proof since I disliked the Korman books as a kid), it's EXTREMELY difficult to get everyone to laugh.
Why? Because, in a joke, you need:
1) Clarity- People must GET the joke, or they won't laugh.
2) Absurdity- A joke is intended to make you laugh about the world.
3) Creativity- everyone knows the joke about the man-eating shark, so you have to delve to find something people won't groan at. Must balance with clarity.
4) Presentation- Corollary to clarity, and a good joke should have either a good storyteller or artist.
Addendum: For pure comedy, you must have ALL of these points present for least 50,000 words in a novel, four or five comic strip panels or 2.5 hours of film.
And thus we see why people laud pure comedy when authors capture it.