Another thread got me thinking that we throw around the word "complex" to describe a bourbon or other whiskey, without really defining just what we mean. Just as taste is subjective, I'm sure what each of us thinks of as "complex" will differ as well. I get the impression that some use the word to describe a bourbon with many different flavor layers, all pleasant in the taster's mind, while others might deem a bourbon complex if there are components that might be unusual at first, but for which one can aquire a taste. In general I believe that tagging a bourbon "complex" is most often a complement, though I suppose a bourbon could be considered both complex and sub-par in the taster's mind.
For me, a complex bourbon will have the traditional vanilla/caramel sweetness with varying layers of floral or vegatative notes presented at different points on the palate. I also think that the "complex" bourbon will have good body and a finish that is not hot, but with just a slight tingle. But the complex bourbon needs that little something extra that makes it a bit different than others on the shelf. Of course, this is my overall description of a "good" bourbon, so I might be missing the point. Here are a few bourbons that I consider complex:
VW 12yo Lot "B"
Four Roses Single Barrel (US Bottling)
Eagle Rare Single Barrel
These are not necessarily my favorite bourbons, but each has a quality that sets them apart from the mainstream IMHO.
So now to the point: How do you define "complexity" with regards to bourbon whiskey? Give a few examples of bourbons that you consider to be complex.