I fly first class a fair bit, and I struggle to get anything done on the plane (in the terminal is fine, though).
For me, there's no way to take a good break on a plane. I can't really get up and stretch my legs (unless you try to pace the aisle), and any kind of distraction is going to be on a screen.
It is more comfortable than coach, but it's still not really comfortable. Coach is actively uncomfortable, first class is just kind of neutral; not actively comfortable or uncomfortable.
I usually get more done sitting in the terminal than I do on the plane itself.