I most recently went through Keflavik twice in October going from Seattle to London and returning home from Paris. The 1 hour layover I found to be quite enough time to grab a quick snack and a restroom break. It was definitely easier on the arrival from the US, as that flight arrived at Keflavik at about 5:30 am, and there were relatively few people around. It was basically a sit around and wait while re-charging my iPhone situation.
The departure took a little longer because of having to clear immigration for departure from Iceland to return to the US, but again, the 1 hr 10 minute or so layover allowed ample time to shop a little at the duty free, get a snack and visit the restroom.
I only thing I find a bit annoying at Keflavik (and this is SMALL complaint because the cheaper fare from IcelandAir means I'll put up with quite a bit), but sometimes the planes can't taxi up to the jetway and you have to deplane the old-fashioned way: by a flight of stairs rolled up to the plane's door, then walking across the tarmac to a bus. I don't know how they would handle such a situation with a passenger who had mobility difficulties, but fortunately that was not an issue on any flight I've been on.