There is a particular quality that makes blues work--you can hear two people play the same lick--when one person does it, it's blues, when another does it, it's just a lick--I used to try and explain this to my blues guitar students, and the best that I could come up with was that they had to learn to touch their strings in the way that they touched a person that they really cared about--not necessarily like a lover(which is the first thing people always think of), but like a child that you were afraid for, or that you needed to be forceful with, or maybe that you were really proud of--
The important thing was that it could be all different sort of emotions--but the most important thing was that it wasn't just smash, thrash, bash, there is restraint and subtly to it--