Coming from a Eurogamer interview...

"One of the things that held it back is despite all of the changes that have happened over the years, it's still one of the more complex and difficult games to play. Even though we do have core fans who are like, 'Oh, I want to have more of this experience,' when you play any other game that has stealth elements, they're all a lot more forgiving than Splinter Cell. I guess Splinter Cell stayed with the most pure approach to that stealth experience." - Ubisoft's Jade Raymond

Raymond also discussed Splinter Cell as a game for those that like to think.

"But Splinter Cell still really is a thinking game. It's really about being intelligent and taking that time in the first phase to plan out how you're going to do things, and understanding the elements, and even planning your gadgets and your load-out and being smart about it. That's where you get the thrill, but it's a different way of playing than most games on the market these days."

Raymond is the dev steering Splinter Cell: Blacklist, which is due to hit Wii U this Summer. It'll be interesting to see how Sam's newest outing comes out with this new focus.