Kind of a dumb trade for seattle, they have already have leon washington, justin forsett, and julius jones. The problem with their run game is not the backs its the line. Besides, forsett has to be better than lynch or atleast better looking...
They didn't have a power runner, Washington and Forsett are more like 3rd down backs, out of the backfield, smaller and faster. Jones used to be sort of a power runner but he seems to have really fallen off.
Lynch is a very tough physical runner. If he has straightened out his off field issues this is a steal of a pickup. He's getting a career best 4.4 YPC so far this year on a bad team with a bad OL, and they were trying to play 3 RB's(like Seattle was) and so the carries came in spurts.
My biggest fear as a Lynch fan would be that Pete Carroll might be the exact wrong coach for a guy like him. Lynch is trying to resurrect his career, he needs a coach who's going to be tough on him, not one who has a history of running a "discipline optional" team like he did at USC or in his prior NFL jobs. One of the reasons so many kids at USC got in trouble while Pete was there was the environment of look the other way Pete put in there, the NCAA specifically cited that when they nailed USC.
Lynch doesn't need a coach who's going to overlook things because he's a good player, he needs someone to be tough on him.
But if Lynch is right in the head he's a very good player and he's only 24 years old.