Not a big surprise. After collecting eight interceptions in his dream 2012 season, Brown tore an ACL in the preseason and missed all of 2013. He had been slated to be one of the Giants' starting safeties last year along with Antrel Rolle, and the Giants like him a great deal. The ACL surely deprived him of the kind of market for which free agents hope, and so it was in the sides' mutual interest to get something done and offer Brown his big chance at a starter's job a year late.
Problem is, that starter's job may not be there for Brown anymore. Will Hill emerged as a very good player at safety for the Giants in 2013, and despite a $9.25 million cap number, Rolle is still on the team for 2014. So Brown would have to beat out Hill (and prove he's healthy) in order to be a starter, as he was projected to be a year ago.
Regardless, assuming Brown is healthy, safety is a real position of strength for the Giants if they have Rolle, Hill and Brown at the top of the depth chart. (I don't expect them to bring back Ryan Mundy.) If Brown makes it all the way back from his injury, as it's believed he will, he offers the Giants insurance in case Hill's off-field issues rear their head again or in case Rolle leaves following the 2014 season.
The Giants also have Cooper Taylor, the safety they drafted in the fifth round last year, who could develop into a more significant part of the secondary over the next couple of years.