What's Angelo Doing There?

Ask anybody to start naming Shakespeare's "best" villains and you're going to round up the usual suspects: Iago, Claudius, Richard III, etc...

How long until you think about Goneril and Regan?  They don't even get a full credit each on this list, they're made to share.  Which is weird when you think about it, because they spend much of the play fighting and ultimately kill each other.  So it's not like they're working together (except in shunning their father).  Does Cornwall, the guy that does the actual eye gouging, even rate?  Nope.  What's a guy gotta do to get some evil credit around here?

The inclusion of Angelo is interesting.  It's not like they were trying to round out a list of 10 or something.  It's always weird to associate comedies with true villains (though I do realize that M4M is a bit of a problem to classify).  I wouldn't expect to see Don John on this list, so how does Angelo make it over, say, Cassius? Tybalt? Is there an "official" definition of villain that we're supposed to use, like how the academy separates "lead" and "supporting" actors?