I've spent a LOT of time in the 767 flat seats. I've never been a good plane sleeper, but I've never had a problem managing at least a few hours of sleep on an EB overnight flight. Yes, they're a little narrow but they are reasonably comfortable. I can sleep on my side and my stomach without much difficulty.

On a WB flight, there's less of a need for uninterrupted sleep, and these seats are very comfortable for reclining.

Also, the 763ERs are a pretty new product... brand new bathrooms with electronic sensors and levers for flushing, washing and trashing so you don't have to touch anything, and among the newest AVOD system. They're also good for couples traveling together as the middle seats are pretty close together while still maintaining enough personal space.