I did this roundtrip in April in Comfort Class and on the IAH-IST segment it was almost 100% full in Comfort, 100% in Y, and around 80% in C.
On the return, IST-IAH, Comfort Class only had 10-15 people in it, Y was fairly full, and C was half-full.
There is alcohol on the flight and the food was actually really good.
One note, when checking-in at IAH, be sure and give yourself a full 2 hours for the process. I showed up 1.5 hours before the flight and cut it close (even using the *G/Business class check-in).