We did Oceania's Istanbul to Athens. 12 nights. We liked it a lot - we loved the ports and the casual ambience and good service. If you search back, there is a review I did of that cruise here if you go back to July 2007

VOYAGER:
MC to FLL 11/07
MC/Dover 6/06
MARINER:
BCN / Ven 10/11
Alaska 2001|2006
Panama Canal 2003
NAV
Caribbean 11/06
Bermuda|New Eng/Canada 6/04
PG 5/05
OCEANIA
Nautica |Ist/Athens 6/07
Regatta|Baltics 6/08
Riviera 2013 Crossing -Istanbul to Miami