1. What does it mean?
헐 is an informal exclamation rather than a description with one fixed meaning. Depending on the news and your tone, it can work like 'whoa,' 'seriously?' or an unhappy 'oh no.'
Also written or said as heol
2. The nuance
It does not automatically mean excitement or approval. A bare 헐 in response to someone's bad news can sound detached; add an actual response when sympathy matters.
3. Examples
“헐, 공연 날짜가 내일로 바뀌었다고?”
Wait, the concert has been moved to tomorrow?
“헐, 네가 이 큰 퍼즐을 혼자 다 맞췄어?”
Whoa, you finished this huge puzzle all by yourself?
Sources
FluentU: Korean text slang guide
References support the meaning and usage. Example sentences are written for NoCapWiki.