An amateur musician asked me what it was like for me, a professional, to listen to amateurs play. What a great question!
And complex.
I would have to say it all depends on the situation and what the amateurs' goal is. If their goal is to imitate professionals I find it stale and lifeless. But if their goal is to have as much fun as possible it is usually a trip to listen, mistakes and all.
When I worked with chamber musicians they were primarily amateurs and I encouraged them to let go of their inhibitions, to stop trying to sound like professionals (i.e., like some CD they had heard) and to react just to the sounds coming out of their instruments, flaws and all.
I learned so much about how composition works from listening in this way. I only wish more professionals would trust their instincts and play this way.
The only thing that keeps them from doing so is competition in a conformity-driven world.