Is a "doozy" a good or bad thing?

I'm interested in the etymology of the word "doozy". And primarily whether it is a good or bad thing?

I always understood it to mean something exceptionally bad.

e.g.

Watch out for that first step. It's a doozy.

But I've just read it used in a positive sense here.

"[Kerber hits a] backhand winner from behind the baseline, that's a doozy."

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.