My definition of a good guitarist is someone who has the ability to play what they want exactly the way they would like to hear it played. Doesnt matter if they get there by knowing a load of theory and the names of a load of modes or whether they use their ear, or feel or by memorising patterns. It's the end result that counts. If it sounds good and its well executed then its from a good player, slow, fast, technical or basic. Although I think the guy who can inject feeling into fast and slow music is the superior player.