Well don't forget old EC. He turns 70 in a few days.
How to tell a great from a good player. A great can do it without making it look hard at all. You see those that are making all kinds of faces, contorting their bodies, flailing around, playing a guitar like it's so hard to do. They may be good.
The ones that can walk out there and rip you a new one and barely move, those are the greats. The guitar is part of them, it flows from the body to the instrument. It's second nature to them.
Old Mr. Clapton is one of those. He doesn't look like he's having an epileptic fit while playing, he goes out, shreds some licks, and walks off. Take a look at a video of the live version of Crossroads, all that coming out of a guitar and him just standing there.
