At first I thought he was going to be like a "low-man-in a yellow coat" type character. Toward the end I just took him (them) at face value. Wonder if we'll get a spin off book about them. They are human, how'd they get that crappy job?
I was disappointed by what the card man turned out to be. I had been expecting something completely different, more ominous, sinister. In fact, I thought it would he would turn out to be a direct adversary--or a direct victim of an adversary.
And I didn't really like the explanation offered for the card man/men, at the end. Everything else in the story had seemed within the reach of believability, as unrealistic as the time-travel wormhole might otherwise seem. But that last bit, about the card men being tied to that job, went too far off into the fantastical for me.
I guess that's probably because I tend to most like stories that are (seemingly) very grounded in reality, in which you are only asked to stretch your imagination a little bit (like in a lot of Michael Crichton).
-- On further reflection, maybe I should amend that last thought: I guess I tend to most like stories ... that start out the way this one did ... if they are (seemingly) very grounded in reality....