Previously noted Superman letters can be found here and here.
Transcript follows.

Transcript
SUPERMAN INC.
480 LEXINGTON AVE.
NEW YORK, N.Y.
Saturday, Feb. 21
Dear Jerry:-
A set of dailies arrived this morning. If there were sufficient time, I'd certainly return them to you for more work; as it is, I shall simply have to have one of the artists here try to do some work on them before we send them to the syndicate. I'm particularly upset, because I wrote you about the same troubles after receiving the last set. It seems impossible that you look them over before sending them out; either that, or you are very complacent about the guy you invented. SUPERMAN looks like a different person in almost every picture, and worse in each. Even if such details as bad hands, bad figures and bad action are passed over lightly, we just can't get away from the fact that SUPERMAN's face is incredibly bad in more than fifty percent of its renditions. I have written you repeatedly about the manner in which his jock strap is drawn, and absolutely nothing is ever done about it. I have no complaint about the backgrounds, which are very well handled, but perhaps more attention is paid to backgrounds than to the figure work. All in all, the sad truth is that after all these years, SUPERMAN is not outstandingly well drawn either in the magazines or in the syndicate stuff. Very discouraging it is, too. And it is getting to the point where I feel that if at least the syndicate material doesn't show a marked improvement, we shall have to consider it "unacceptable", and make other arrangements to have it done.
Incidentally, I note too that some of the editorial changes in the dailies are not being made.
Altogether, the situation is serious enough to warrant your doing some real worrying.
(Signed, 'Whit')