I don't see any recent comments on Iceland Air, so I'll post about our recent trip. Iceland Air began flying from Denver not too long ago, and we were able to book tickets for our trip to Europe for a reasonable price. Overall, we were pleased with the service. Flights were on time (although takeoff was delayed once for close to 10 minutes because it took so long to board), baggage was handled efficiently (except in Paris, where it took forever, but that's probably the airport rather than the airline), attendants were polite and professional, and we rather liked landing in Keflavik to break up the trip a bit, walk around, get a bite to eat, although it added time to the trip. There was a good selection of free movies and TV, but if you go, remember your headphones because they don't provide free ones and the ones for sale were 8 euros. I also recommend taking some food, because the food selections are limited and seemed pricey for what you get.
Iceland Air allows a stopover in Iceland at no extra charge, which is a great way to bring some tourist dollars into the country. The negative part of this is that travelers are really hit with marketing, tour opportunities, shop duty free ads, etc. We did stop over for one night on the way back, and I would probably not recommend it unless you have at least two nights to spend. It is expensive to get from the airport to anywhere, whether you rent a car or take a shuttle bus. And unless you have a full day to spend, you probably won't have time to fit in any of the guided tours. We rented a car from Budget at the airport with no problems, and had time before our flight the next morning to drive to Pingvellir National Park (sorry if I've butchered the spelling) just to see some of the countryside.
I said we were pleased overall, but if we had rated this trip after the first leg from Denver to Keflavik, I would have said it was terrible and we would never fly with this airline again. The problem was that the first plane we were on was extremely cramped, with zero leg room. Flying economy, we didn't expect luxury, but the seat rows were so close together on this plane that one could barely get into and out of the seats. We are not tall people--I'm 5'6--and my knees were touching the back of the seat in front of me. On most flights I've experienced, you can unbend your legs a bit and stretch them out under the seat in front of you. This was impossible on this plane, even for someone of my height. Iceland Air's website says their economy class legroom is 32". I compared that to Frontier's economy legroom, which is listed as a minimum of 31". I've flown Frontier and Southwest a number of times, so I have those experiences to compare. There is no way that there was 32" legroom on the first leg of our Iceland Air trip. On the other 3 legs of the trip, the leg room was much better, probably the 32" as stated.
The other complaint I have is with the boarding procedure. There is none, it seems, or at least there wasn't any particular standard procedure on our 4 flights and it seemed chaotic in comparison to many other flights I've taken. They did board a passenger in a wheel chair first, but on most flights they board families with children or others who need assistance first, or at least after the first class passengers. This did not happen, nor did they call for any particular rows to board in order.
If we fly to Europe again from Denver, I would consider Iceland Air only if the cost was considerably cheaper than other options unless I wanted to take advantage of the no-extra cost stopover to visit Iceland for a few days.