The iOS app had an update a couple of months ago to improve the typography. Everything else looks like crap now by comparison. Depending on which FireHD you have, they will be updating that as well, as with currently shipping Kindles (and PW2). They say at
http://www.amazon.com/b?_encoding=UTF8&node=11516960011 that 'Fire tablets' have this feature (last two generations do have Bookerly font and one sees the occasional book with hyphenation), but I don't think they are done yet. Still seeing a lot of line spacing and margin variation that doesn't happen on iPad.
They are also updating the catalog of ebooks for further improvements, though it is not clear they'll complete that at any time soon. If you look at product listing for Kindle books on amazon.com (with desktop browser), some will show 'Enhanced Typesetting: Enabled'.