Last week, Gamespy did an interview with Warren Spector on Deus Ex: Invisible War.
"GameSpy: Games are becoming harder and harder to pigeonhole into genres, and Deus Ex leads the pack. Do you think it'll become necessary to create entirely new ways to classify games?
Spector: I think from a development standpoint, categorizing games... who cares, whatever. Call it whatever you want. The marketing guys sure would like to be able to categorize stuff. And interestingly I think the increased attention being paid to games in universities and colleges around the world now is going to result in people trying -- and succeeding, frankly -- to put games into categories. So I think you're going to see more precise language describing games, and you're going to see more people thinking about this. But I don't think it's going to impact developers much at all. We don't think "Let's make a shooter / role-playing / strategy game..."
GameSpy: ...With card-battling elements!
Spector: Yeah, there you go! So I think you're going to see it, but the developers aren't going to lead the way, and aren't going to think about it much."
It is important to distinguish between genre (the classification of games) used for development, and genre used for audience segmentation (i.e. what is used by retailers, marketing, the press, etc.) The first is design shorthand, the second tells you something about your competition and the expectations of your target audience. Confuse the two, and you limit your choices for no good reason.
Today, Gamespy published an interview with Harvey Smith and Ricardo Bare, again on Deus Ex: Invisible War.
Both interviews discuss game design in general and in Deus Ex 1 and 2 in particular. I recommend reading them.