Some of you may recall the leap that Marquis Johnson made from 2008 to 2009 relative to performance. He was the obvious weak link in the secondary in 08, but in 09 he led the team in pass break ups. It was impressive to see a guy work hard at his craft, and literally work himself into a fine DB. (was actually drafted in the 7th round)
With that said I cant really recall a player improving as much as Henry has. He has become a force. His vision, footwork, explosiveness, blocking, etc., etc., ... his entire game he has taken to an elite level that honestly I did not think he would be capable of when I watched him early in his career.