Chuck's character development has been there, despite what Temis says. The thing about Chuck is that he lets the women in his life pretty much dictate what he does as he tries to please them all. This is why he is seemingly changing back and forth as to whether he wants in or out of the spy business. He is basing what he does on what Sarah, Ellie and even to some extent General Beckman want him to do. Or what he thinks they want him to do, then he finds out different (even though he may still be wrong) and hence his change in direction. And all that can be traced back to abandonment issues Chuck has with his parents, and primarily his mother. He feels guilty. That it was his fault their mother left them. Even though that last bit about their mother was added with the season finale, it fits in really well and gives a compelling psychological reason for Chuck's varying motivations.
Another bit that was added in that episode, Stephen Bartowski's spy shop hidden under their old house in Encino, also has the potential for providing story lines to last this show for years. Every case file they flashed across, like Operation: Corvus for instance, is another potential story arc for the show to take. The one that says "Identity: Orion" is a potentially good reason to have Scott Bakula back in flashbacks as Chuck unravels the hows and whys his father became known as Orion.
So I can see this show lasting many seasons, not just one or two more. Because this team of writers have shown they know enough to keep the show fresh by injecting some unexpected changes (like the comic teaming of Casey and Morgan as a spy team. Who saw that coming a season ago? I sure didn't) along with giving the fans what they want, like Chuck and Sarah finally together and for keeps. I am confident of their success because they have put out a show that has only been getting better and better as they go along. As the Chuck discussion threads have shown they have a consistently high ratio of "Awesome!" ratings week after week. So I think this show still has a lot of legs. I think it may wind up lasting as long and being as well regarded as Seinfeld or Friends.
It hasn't been what I would call natural and organic.
