Hopefully someone in your deans office can give you a hint if your other letters are strong. This one obviously is not and I don't think it is safe to assume the letter is strong either. If it is this flat, I would just find someone who can be more enthusiastic about you.
Physicans are a strange bunch, and some don't have the balls to tell you they are not able to write you a strong letter. I ALWAYS asked the people who were writing on my behalf "CAN YOU WRITE A STRONG LETTER IN SUPPORT OF MY APPLICATION." Anything other than an enthusiastic "yes" and I moved on to ask another person. Recently when transferring from my program I was given a copy of my file, including those letters, and it seemed to have worked.
I think by cc-ing you the email, he was taking the chicken **** way of telling you the letter was luke warm. You need an attending who has worked with you who can speak to your potential as an intern or resident.
Once upon a time my friend asked a very two-faced attending to write her a letter. He had been very nice to her up front, but the letter was a real back stab. The nice lady in the dean's office who scans the letters in actually paged her to advise her not to include the letter.
I would not hesitate to ask around your dean's office if your other letters are decent.