Despite its spelling, it is used more like "Hell as Fuck" in both meaning and pronunciation- etymology and anthropological studies suggests that the "ass" was probably just added to increase the vulgarity of the phrase. It is used as a descriptive phrase to describe any noun which is "Hella Good/Bad" as "Holy Fuck", it can be used to describe both good things and bad things depending on context and how it is said- this is indicative of its origins as spoken vernacular.
That show was Hell ass Fuck! Shi-it!
by The WangStein October 11, 2005