I think that cool has at least a little something to do with how much more stuctured GaGa's songs are. The melody/music is a lot more structured, for one -- in a lot of Ke$ha's songs, I found it difficult to tell when the verse was ending and the chorus was beginning as I listened to it for the first time, whereas I could always tell with GaGa (and of course GaGa's beats are much more rigid). But the vocals are more structured as well -- they both have tracks where they just singsong their way through the verses, passing time till the big chorus, but GaGa's singsong, like her beats, is more rigid and even. The overall effect is that GaGa feels cleaner, more stylish than Ke$ha.