We’ve flown them several times, always connecting thru Reykjavik if we’re headed someplace else, but also used them for a vacation in Iceland 3 years ago.
For getting from Denver to other places in Europe, they’re really giving British Airways, Lufthansa, and United a run for their money. So is Norwegian Air, with stricter carryon luggage policies, and extra fees if you go over their tight weight limit.
But Icelandair does offer food on board, but at least in coach class, you pay for any of it you order. We’ve taken salads in a plastic domed takeaway container on board (just don’t have more than 3 oz. of dressing to make it thru security at the airport) and our own bottle of water, which they will top up onboard. Icelandair is efficient and, as you noted, relatively cheap.