I was asked to provide feedback on our experience with Norwegian Airlines. I can't find that thread again unfortunately, so I'm posting here.
We flew from Oakland to Gatwick then to Rome. We returned from Rome through Stockholm, landing back in Oakland. We traveled in June 2016.
Overall I would say it was okay, which is about the same as most airline experiences I have had in the last decade.
Our flight out of Rome was moved forward about two hours a couple of months after I had booked and and although they offered the option of canceling all my flights, it was really too late for me to find a low airfare elsewhere or shift my plans around. That meant a very early arrival at FCO and a five hour wait in Stockholm. Not long enough to leave the airport--at least not for me as I am risk adverse when it comes to possibly missing a flight. And a rather long time to wait. I wasn't thrilled, but what can you do.
We pre-paid for checking one bag per person and for meals. The meals were horrible. Truly horrible. My thirteen year old ate almost nothing--just a couple of bites of rice each way. I'd suggest skipping the meals and just bringing your own food on the plane. Also the shorter flights within Europe, they do not offer any free drinks--not even a cup of water. So buy a drink after you clear security and carry it on.
The flight attendants were fairly brusque. Not exactly rude, but not warm or friendly or helpful and mostly absent from the economy cabin.
They charge for blankets so bring your own if you want one.
The in-flight entertainment on the international portions of our flights was good. Lots of choices. As I recall there was no screen on the shorter flights within Europe (smaller, older planes).
The seats seemed fairly standard to me. We booked early and did pay to be able to pick our seats. Since there were just two of us, we chose the second row from the back which had just two seats together. That was great except we were last off the plane and that meant a long wait to clear immigration on the US end of the flight.
Try not to gate check your bags as, despite being told otherwise, they did not return them plane side at FCO (Rome), instead we had to wait for them at the baggage carousel. I gate checked ours voluntarily because they were practically begging people to do so. I would not do that again! We deliberately checked our bags all the way through on the return trip and they arrived just as expected.
All in all, I would take Norwegian again if the convenience and price worked out, but I would not be super excited or pay more or shift plans to fly with them.
Hope that helps.