I've finally figured out what has been bothering me about the Mark Greene storyline on ER: Anthony Edwards simply looks too healthy. I've been around people with terminal cancer before, and they do not look as healthy as Edwards did on last night's episode. Terminal cancer patients lose large amounts of weight very quickly and they generally take on a pallid look as death nears.
I'm also irritated a bit at NBC's rather cynical promotion of the whole thing. They ran ads all week touting Greene's "last night in the ER", clearly trying to imply that last night was his final appearance on the show. I may be proven wrong, but I doubt it: we will see him again during May sweeps, and there will be ads galore imploring us to "say goodbye to Dr. Greene".