After the interview, it is always a good idea to reply to feedback. Whether or not you were offered the position, you should reply the mail you are sent.
Make the email short and courteous. Thank the recruiter for the opportunity, and if possible, ask for tips for your next interview.
Recruiters have been known to change their minds at the exhibition of this kind of behaviour as it shows the applicant has a good attitude and a teachable personality.
Even if this doesn’t happen, at least you get tips for your next interview!