I agree with you Sherlockian. excellent acting can often be overlooked because a good actor makes things look effortless, as an observer you forget thay they are acting and don't see the work that has gone into their performance. Whereas with average and mediocre actors you are aware of the process behind what they are doing, you are aware they are pretending..
However the diferrence between 'acting' and 'pretend' is a tricky one. One the one hand the actor is pretending to be someone other they who they are and yet what they are feeling and showing is real.
For instance I am currently rehearsing a play in which one of my sons is killed within the first few pages. When that happens i do feel and show the emotion but it is within the confines of the play - I personally don't use my own experiences i.e think about an upsetting time or event when trying to play the scene. For me the emotions come out of the writing, the scene, the character I'm playing. It is that character's emotions, not mine. So I am kind of pretending but I'm kind of not. I am acting. Hopefully well enough that people will see the character and their pain and not me.
I haven't really described that as well as I would have liked but I hope it makes sense. That's the other thing with acting, although it can involve a lot of hard work it is also spontaneous, of the moment, intuative and fleeting. Things that can be hard to pin down. That's what makes it such good fun though!