The issue with that's it changes Sam's character in no discernable way, in Double Agent anyway, only in superficial ways.
The original Xbox version takes more advantage of it than the Xbox 360 version, but does not stick the landing with Enrica, because it is confused about whether she ought to be an authentic romantic interest or not.
Whereas she should have been a surrogate daughter, that might have more interesting strained Sam's loyalty, and it's just not explored enough.
I really like the first three, but find Double Agent by far the most interesting one, especially with not much known about the development.
Both halves of Double Agent have some truly great stuff, and the concept of being one has the most potential out of anything the franchise did, I want to see that one not just remade but entirely rethought.
Conviction's more Taken than Tom Clancy, and it's barely Splinter Cell anymore, Blacklist tries to ride the line but comes away feeling well executed but generic.