I'm sure you know of this feeling. When you find something very funny, but it doesn't make you laugh out loud. Perhaps it's even "funnier" than other things that make you chuckle profusely. What is a word to refer to this phenomenon specifically? If not a word, then an expression is also acceptable.
I would probably use amusing for this. From your description, I'm imagining a story or something else that is entertaining and has a humorous tone, but there's no one specific thing or moment that makes you laugh the way that the punchline of a joke does.
There are some more specific words that apply to certain cases. For example, this is how I usually think of the Mel Brooks film The Producers, about two men running a scam that involves producing the world's most terrible play - it's not funny because of jokes or one-liners, but just because their situation becomes increasingly absurd and ridiculous. In this case, the word farce fits well.