Im talking about the ones the did a great performance, but when improvisation is added specially on the solo parts people start criticizing because it missed some notes or it didnt sounded like the original. isn't what covers all about? be original and improvise if you can?
Hmm.
You ask, "Why do people criticize...?"
Well, firstly because they're humans, and humans do that kind of thing.
Secondly, because they may not have the same
expectations that you have, re: covers. The idea you express ("isn't what covers all about? be original and improvise if you can?") is exactly the kind of thing a
creative musician tends to say. But a
club owner who's just trying to keep the patrons happy (so they keep buying drinks) doesn't care about that at all. If "be original and improvise if you can" keeps the patrons buying, he
would subscribe to your idea. But maybe it doesn't. If "make it sound exactly like the radio cut playing in the background" makes the patrons happier and spendy-er, then the club owner will prefer
that approach.
Thirdly, because the kind of person who
even notices the improvisation and the originality is not a
normal audience-member. He is more likely to be a "close listener," who is more analytical than a typical audience-member. And with
that kind of listener, you run three (interrelated) risks:
1. He may know the original note-for-note, tone-for-tone, and be anticipating a particular passage he especially loves. If he doesn't hear it, he'll be disappointed.
2. He may not, as a matter of taste, prefer the changes you make over the original. After comparing them in his mind, he may be disappointed that you didn't (in his own opinion)
improve upon the original, but merely
detracted from it.
3. He may be a musician, or someone able to tell whether your version requires more or less skill than the original. If he
suspects that the reason you departed from the original is because
you don't have the skill to play the original, he'll be disappointed because it makes him aware he's listening to an inferior musician. (This applies even if you, yourself, are actually quite good.)
None of that means you have to surrender to these other persons' viewpoints and play every cover note-for-note.
It just means that you shouldn't be
surprised if they
aren't perfectly thrilled, when you opt to follow the instincts of a creative musician, and they weren't expecting you to do so.
P.S. One way to overcome the disappointment of the "close listener" is to play
both the original solo
and your own personalized extension of it, increasing its overall length. (Alternatively, you can play the original solo during the bridge, but take an outro solo that you customize.) By doing this, you assure the "close listener" that you're not departing from the original due to inferior skill, but only because you have
at least as much skill as the original artist, plus some
additional "things to say." (But make sure your additions are "tasty!")