Marbury's being trashed and underrated here for the most part (speaking only of on-court performance since I know nothing about off-court). 20 games isn't nearly enough. I thought he did as good a job as could be expected given the short time and very short minutes (no choice). He played hard on defense, too.
His only problem was shooting and hesitancy shooting, and I think those were do to rust and trying to fit the role of small-minute backup (everything magnified). I think he'll do fine as a starter somewhere next season, but I don't think he fits well with the Celtics as a starter. We need full-court speed, not just drive to the basket speed.
He's not washed up. He's had too much rest for that.