1. What does it mean?
A playful combination of 꿀 ('honey') and 잼, shortened from 재미 ('fun'). It praises something as very enjoyable, whether that is a game, a show, a conversation, or a day out.
2. The nuance
'Hilarious' is only one possible translation. An absorbing game can be 꿀잼 without being a comedy. The contrast with 노잼 is about how enjoyable the speaker finds something.
3. Examples
“기대 없이 시작한 게임인데 완전 꿀잼이야.”
I started this game with no expectations, but it's so much fun.
“어제 보드게임 모임 꿀잼이었어. 다음에도 가자.”
Yesterday's board-game meetup was a blast. Let's go again.
Sources
National Institute of Korean Language
References support the meaning and usage. Example sentences are written for NoCapWiki.