As just posted, Norwegian are back with more amazing sale fares to the USA (starting at £162 Return!) direct from the UK. I'm due to fly on the new 737-MAX with them later this year - any ideas yet what it might be like?
In economy or their premium / business class (=~ premium economy)? A friend did premium from Boston to London overnight, having mostly just flown economy with legacy carriers, and really liked it. Otherwise, make sure you're aware of what is and isn't free, and plan accordingly!
I just fly Norwegian JFK-LGW in economy. It was fine. I watched a film and then just tried to sleep as much as i could. They turned the lights up and started serving breakfast more than 2 hours before landing. I couldn't sleep more after that.
Food service is different also. They don't go around offering everyone food, which takes a long time. You can pre-order food. Not many people on my flight did, so it didn't take long to get food if you pre-ordered. Also, you can order snacks from the seatback screen.