I have done transatlantic segments on the 752 many times, and BF is quite comfortable, but the entertainment selections are not as good as the 67s or 777. The service on the 752s seems much more personal because there are only 16 seats, and the flight attendants seem very efficient. Maybe its just a perception, but most of the 752 flights, there have been three flight attendants in the BF cabin, with on FA manning the galley and the other two having eight seats each to tend. Much smaller passenger:FA ration than on the 67s and 777.
I don't know what it is about the 752 BF seats, but a higher proportion of those seats seem to have problems vs. those seats on their 67-series cousins. On any given flight on a 752 BF to Europe, there has been at least one seat that has malfunctioned or is not working completely. I cannot say the same about the 67s/777s.
The longest segment I have ever done on a 757 personally is EWR to AMS not long after 9/11, and it was very, very cramped for a flight that long. I cannot imagine having to do that for even a half-hour longer, say EWR to Berlin or Hamburg.