Hi Anonymous,
It's a pity that most firms don't really share a lot of feedback after interviews, but in any case it's good to chase them for future further improvement.
Instead of emailing, I would rather try to catch them on the phone - an email or letter is just so easy to ignore and gets easily lost in the daily hassles versus being on the phone and asking directly. Chances that you really receive a lot of useful feedback is oftenly low, but as indicated before definitely worth the effort in my opinion!
Hope that helps - if so, please give it a thumbs up with the green upvote button below!
Robert