Well, at 6-foot-4, 230 pounds the good obviously for Brandon Marshall is his ability to catch the football and make plays on the field. This guy is the scariest looking receiver I've ever seen running with the ball. He runs like an angry man, as shown in this video below.
And as for the bad, Marshall has shown a history of unpredictable behavior, and several off-the-field incidents have taken place during his four years in the league, with an example shown here.
So the Seahawks will have to weigh the good with the bad in making a decision to bring Marshall to Seattle.