Just for the sake of comparison...
In 2008, Hillary Clinton -- who was widely considered to be a major player and contender for President (and was a contender) got 29% of the vote in a 6 way race in Iowa.
In 2012, Mitt Romney got 25% of the vote in a 9 way race.
You can insinuate that this is a bad showing, but it is not.
considering its been no secret that Iowa was never a priority for him (while being very much of a priority for several of the others) a win however narrow the margin is remarkable.