russel is maybe the most underrated actor working today.
i lost all interest for sg1 when jackson died and then came back miraculously when ratings began flagging.
Actually, the show's ratings were doing fine during the sixth season with Corin Nemic in for Dr. Jackson. Shanks left the show because he was becoming burnt out on the character and because he felt that the idea that it was originally a kind of buddy show between him and O'Neil was going away under new writers. He preferred the buddy moments with RDA.
There are many reasons why he returned (they "killed" him off in a way that he could return, that was clear and I'm still not convinced it wasn't meant to be a one season deal to begin with). First main reason is that fans clamored for his return, not only to the studio and show runners but Shanks got letters asking him to come back. Funny thing is, that Nemic had grown a large fanbase himself on the show and when they announced Shanks return, many were hoping they would keep Nemic as well. When they didn't, the Nemic fans became upset. Just goes to show you can't please everyone.
Bringing back a character because of fan outcry has happened on more than one occassion in the SG universe, the first being the biggest, Shanks return to SG-1. The second was very small and was Nemic's return for an episode or two. The latest has been the return of Paul McGillion this last season on Atlantis. While it's good that show runners respect fan views and desires and that they listen to their fans (something Berman never did on Trek and cost him is job -- way past the time it should've), there is a fine balance. A good use of this balance was the return of Dr. Frasier (Teryl Rothery) for an ep of SG-1 after her brutal death (she died in what is probably the best 2 eps of SG-1 ever made and if you stopped watching at the 7th season then you missed it as well as some of the best SG-1 moments ever in the series). They brought Rothery back for only one ep and it was clear it was a different Frasier from a different parallell universe. They also didn't over play it when she appeared.
All of that said, the other reason that Shanks returned was because they clearly offered him a chance to expand his ability to play different roles. In the season after he returned, they had Dr. Jackson doing things that allowed Shanks to be challenged and play characters other than Jackson, sometimes within the same ep. The main one that comes to mind is when Jackson became the vessel for the minds of a ship of colonists who had died in suspended animation. It was an amazing performance by Shanks.
To say they brought him back because of flagging ratings, isn't fair. Personally, I'm glad he came back. Since RDA left the show, Shanks has kind of taken over his role as the center of the team. His growth as a character was subtle but true.
CE
It did seem rather abrupt for a season final. 
