I, too, think that the voucher is inadequate. I'm on 841 next week JFK-HKG in F. 15 or 16 hours is a mighty long flight, even more so without AVOD. I tend to watch several movies, along with the odd Family Guy episode, probably use AVOD for a little more than half the flight. Yes, I do read, but I watch a lot of AVOD. These long flights are my opportunity to completely chill, do mindless things, free from my usual tethers (SMS, e-mail, phone, etc.). One of my decision drivers for CX (compared to BA, for example) is the quality of the AVOD.

That said, though, they still got you there, and safely, too. I'd say that an upgrade certificate would be more appropriate, -- i.e., give you a little extra service on your next flight to replace the service which you did not receive on your last one. Seems reasonable to me.