Having only heard the album Viva Santana and whatever the radio stations decide to play prior to purchasing this album, I think that Supernatural is a very strong album; despite the fact that radio stations drove Smooth into the ground.  Since, by my definition, I am not a fan (being both familiar with and liking at least 80% of a band's music) of Santana, I am not biased by the same factors a fan (by my definition) would be.  I think that the collaborations are great!  They add a slightly different flavor to the mix.  Looking back, even Viva Santana varies from rock to progressive to latin etc.  So, I see no problem with collaborating; though he (Carlos) definitely chose some strange people (except Matthews and Clapton).  However, they do not take away from the quality of the music.  There is not a single weak track on Supernatural!  Even Smooth is great (just played to death).