Is a "doozy" a good or bad thing?

According to the Oxford Dictionary of English Language, doozy means,

something outstanding or unique of its kind.

it's gonna be a doozy of a black eye.

Edit:

Here is what wikitionary.org has to say about the etymolgy of the word doozy also spelled duesy:

American, from daisy (the flower), also 18th century and onward English slang for something excellent. May have been influenced by Eleonora Duse, Italian actress.

The same source goes on to state:

(US) something that is extraordinary. Often used in the context of troublesome, difficult or problematic, but can be used positively as well.

Most of the test was easy, but the last question was a doozy.

A Zulu word meaning "close, next to, near; nearly; alongside; close shave".

We used this word in Rhodesia in the meaning "close shave" when conversing in English.

That was Duzie.
= "That was close", e.g. "He was nearly bowled out".

When comunicating with the Africans, we referred to all the Zulu meanings in the correct context of speech.

"Doozy" is often used to mean "troublesome" or "problematic," but it can also be used with a positive meaning. It means "extraordinary."

It's probably an alteration of the "daisy" flower, and started in 18th-century England as a slang word.