Watch the The Four T's online guitar lesson by Jeff McErlain from Blues Survival Guide: Rhythm Edition
What makes a great player on any instrument? That's a great thing to think about when we are listening and practicing. I am looking for 4 things: someone who plays in tune, in time, has a great touch, and a great tone. I feel that one often informs the other because all of these attributes make us take a close look at our playing. I don't feel a lot of these things are taught enough in schools of by our teachers in general. Of course there are exceptions but I don't remember many of my college professors discussing how important these things are, we'd analyze the notes, harmony, technique, etc but not the essence of the music. Technique is not how fast we can play, it is how in control we are of our instrument. I love players with great technique on any instrument. To that point, please listen to as many different instruments as you can, I know I have learned a lot from horn players alone.