Weirdly enough, I think Ibrahimovic is underrated, simply because he spent the peak of his career in Messi and Ronaldo's shadow. His scoring record is stratospheric, an unusually high proportion are worldies and he's succeeded in almost every major league. Until he came to England he won league titles everywhere he went.
Still, it feels like people put, say, Ronaldinho, significantly ahead even though they should be regarded as - minimum - the same level. Few people in the history of the game have been as dominant on the pitch as he was.