Wow. I think I actually felt my braincells dying as I read this article and the responses to it.
Much like beauty, genre really is in the eye of the beholder. This is not taxonomy, for fuck's sake. We're all smart enough to use the Internet, so theoretically, we should be smart enough to make some determinations about how a game is constructed from the blurbs on the back of the box without relying upon an arbitrary label placed upon it by some marketroid who thinks that "it'll be more popular if it's a ______ game".
Ignore the 'classifications', except to use them for a quick and arbitrary sorting, and if you're someone who uses quick and arbitrary classifications to make your purchasing decisions, well, I have some DLC of a bridge in New York I can pass on to you, dirt cheap.
EDIT: oh, and yeah, Borderlands is shit as a single-player game. Redundant and nothing particularly new or innovative. The story is occassionally entertaining, but not to the point where it actually merits the time investment.
Multiplayer, however? We had a pretty good time. I don't know if it was 4x $60 fun, but it was an enjoyable few hours with my friends.