the stanleys !
in answer to 'is it worth?' - YES
we really liked Kyrgyzstan, fabulous.
Kazak - big ! with the capital of Almaty - expensive!
Uzbek - absolute must if you want the 'silk route' classic cities.
Turkmen - mmmmm interesting, i would say well worth experience but my advice would be do enter under a 'transit visa' and NOT book a 'tour'.
check my website and the download pages for some details. : www.travel.uklinux.net
loi's ???? changes regular, my advice here would be cotact David at StanTours, he's the 'man on the ground' he will be best to advise and help i think.
'ferry' on the caspian - this really is an optimistic description ! there's a regular boat and they take vehicles but you can't really call it a ferry!!!!! we crossed from Azerbaijan to Turkmenistan on one of the 'daily' boats for the '15' hour crossing. Of course we ACTUALLY waited 2 days for the 'daily' ferry and it took 36 hours to make the '15' hour crossing !!!
Not a complaint, in fact fabulous experience !