AbFab is better known on this side of the Atlantic because Comedy Central aired the living SHIT out of it in the 90s, and it became quite popular, whereas Blackadder was generally relegated to PBS. That said I DESPISE AbFab. Hate it. I thing it's screamingly unfunny shit, and it took years for me to discover that Jennifer Saunders was actually capable of being moderately amusing. Blackadder, however, is genius.
I think Blackadder was indeed a great show. But I am glad it ended when it did. I felt series 4 was starting to get a bit formularic. Have they ever had Alan Partridge in the US. Or the great Chris Morris shows. The day today or Brass Eye?