I've flown FI once JFK-KEF-JFK and about five LHR-KEF-LHR trips (and six or seven domestic / Greenland flights). The majority of the flights have been memorable for their sameness: same meal, same video showing in-flight relaxation exercises, same on-time service - it's almost a little scary.
Catering is all right, and I think soft drinks and water are free on No Am routes. Blankets and pillows are available, and the crew are friendly, but not excessively so.
I like FI, and like KEF because it looks chaotic but works so well.