a/one hell of a...

a hell of a someone or something

 and a helluva someone or something 
1. Inf. a very bad person or thing. (Use caution with hell.) That's a hell of a way to treat someone. He's a hell of a driver! Watch out! 2. Inf. a very good person or thing. (Use caution with hell.) He is one hell of a guy. We really like him. We had a helluva good time.
See also: hell, of
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

hell of a

Also, one hell of a
1. See devil of a.
2. This phrase is used as an intensive to emphasize certain qualities about the noun it modifies. By itself the idiom is ambiguous, for its exact meaning depends on the context. For example, He is a hell of a driver can mean either that he is very skillful or that he is a terrible driver. Similarly, We had one hell of a time can mean either that we enjoyed ourselves greatly or that we had an awful or difficult time. [Second half of 1700s]
See also: hell, of
The American Heritage® Dictionary of Idioms by Christine Ammer.

a (or one) hell of a —

used to emphasize something very bad or great. informal
1990 Stephen King The Stand If someone on the committee has been leaking, we're in a hell of a jam.
See also: hell, of
Farlex Partner Idioms Dictionary

a/one hell of a...

(spoken, slang) somebody/something that is very bad, good, unusual, impressive, etc: We had a hell of a good time at the night club. I had one hell of a hangover the next morning.
This is sometimes written as ‘a/one helluva’.
See also: hell, of, one
Farlex Partner Idioms Dictionary
See also:
  • scare the hell out of someone
  • helluva someone/something
  • play (merry) hell with (someone or something)
  • play hell
  • play hell with
  • play hell with somebody/something
  • play hell with someone/something
  • play hell with something
  • give hell to
  • a hell of a