Marshawn is doing the right thing. He is obviously breaking down at an age where even non-physical backs start to break down. And he's the most physical back the NFL has seen since Jerome Bettis.
I agree with your point, way better to see a star retire in his good years before he sullies his legacy with poor performance. Barry Sanders understood that. So did Ray Lewis. Calvin Johnson evidently understands it. Hopefully Peyton gets it. Guys like Emmitt Smith did not.
And that run against New Orleans was probably the single best run I've ever witnessed. Though Barry had quite a few, just of a very different variety.
I really liked Marshawn too. He was a very popular player to hate because of his perceived bad attitude, but I think he was just a guy who didn't want people bothering him. I bet he's a cool, funny guy for people who know him.