Infamous: Second Son broke into the Amazon Top 20 Best Sellers of 2014 list. Note that this chart is not the same as "Best Sellers". That simply makes an hourly comparison of how the items sold versus each other. This list is actually showing how they've ranked in total sales for the year. Yesterday Infamous was in 26th place making this a significant jump. Metal Gear Solid V: Ground Zeroes for the PS4 is currently in 14th after being in 17th yesterday.
As for how the games have performed on Amazon just for this month so far, Infamous is currently in 7th place with Ground Zeroes for the PS4 right behind it in 8th. The PlayStation 4 is in the top spot so far. PlayStation Store Gift Cards continue to sell ridiculously well being in three of the top five spots for March and three of the top four spots for the year with the $20 card at the top spot.
Amazon charts do not represent any highly accurate metric for how total market sales are going but it is useful to gauge excitement over products as enough people buy from Amazon to be a useful statistic.
http://www.amazon.com/gp/bestsellers/2014/videogames/ref=zg_bs_tab_t_bsar
http://www.amazon.com/gp/bestsellers/2014-03/videogames/ref=zg_bs_tab_t_bsar