That's a doozy.

That's a doozy.
That's a doozy" likely originated from the "Duesenberg" luxury automobile, which was outstanding in its time. Today, the phrase refers to anything particularly impressive or extraordinary, standing out from the ordinary.
Wow, that's a doozy of a story you just told me.
The speaker thinks the story just told was very remarkable and impressive.
That storm last night was a real doozy, wasn't it?
The speaker describes the storm last night as very intense and remarkable.
When she described the situation, I knew right away that it was a doozy.
When describing the situation, the speaker immediately realized it was very remarkable and intense.