I have always found it to be one of the easiest to drinking whiskeys available. It's one of my favorites! At the risk of getting a lecture on the proper way to drink whiskey, I like it with a single ice cube.
I've always found it very smooth, with quite a lot more body than regular Bushmills (or Jameson's). Great neat, on ice, in coffee, over ice cream, whatever you like. It's been a big seller than the 1930's, if I'm not mistaken...
However, YMMV of course - the final verdict on each man's booze is his own.
Pretty smooth to me among the Irish whiskeys. My favorite until ones starts getting up into things like Red Breast. Most Irish whiskey seems fairly smooth to me. Black Bush seems more flavorful to me than many Irish. I think it is aged in sherry barrels or something and is a "single malt," the latter is unusual for Irish.