Just flew WOW a few weeks ago to Iceland as well (got back 6/9), from Boston though. Actually pleasantly surprised overall relative to what I had heard and was expecting. Backpacks weren't weighed at all or even looked at and they barely looked at the weight on my checked bag. Flew WOW back from KEF as well and even there, they didn't weigh my backpacks. My checked bag weighed 21 kgs which was over the limit so they just told me to move one item to my backpack and cleared it - apparently 20.9 kg is acceptable to them.

Only downside is that we had about a 3.5 hour delay due to a flight controller strike and they didn't communicate it until we were on our way to the airport which was too late. It was madness at KEF due to all the delayed inbound and outbound flights, but not really WOW's fault.

I'd fly WOW again as well if it was convenient. I too tried to book the Radisson Blu 1919 but it was unavailable so I booked the Radisson Blu Saga which was pretty terrible. 70's decor and lots of construction. But each of the hotels we stayed in on the Ring road was worse - basically expensive hostels...but I suppose that's not why people go to Iceland.