Now I've never listened to Gaga, so I am working off a point of unfamiliarity here, but I think we should all be more open to other types of music. From what I can tell, of all genres, rock/metal fans are the most resistant to any other type of music, and I think it reflects badly on us. That is not to say of course that there are some rock fans who enjoy other genres, but just watch a rock video on YT and you'll see the hate towards other genres, pop and rap in particular in the comments.
I actually do like some rap, and I think it's not too different from rock really. They're both music forms that express (mostly) forms of anger. I do find it harder, though, to appreciate rappers that use computer generated instruments and sample other songs. That's why I like Eminem; for example, I love that killer riff in Lose Yourself:
http://www.youtube.com/watch?v=hO2wA0Te0wM
That song has some great rhythms and I could actually see it working as a rock song. Also, his lyrics have some real meaning, unlike very many other rappers.
I think you just have to be in the right mindset to appreciate rap. Just be open is what I'm trying to say.