"Meet Joe Black" does not have a great plot. It does not have an original plot. But originality is overrated. I do not agree with the above noder, and I think the acting is very good; I'm not exactly sure how a person who does not watch many movie judges what good acting is, but that's besides the point.
What makes "Meet Joe Black" a good movie, IMO is that it is much more actor driven than most movies are. This is why the plot is superfluous. This movie is more form than substance, as the characters never really develop, unless you count Jack's cheesy change of heart at the end which the above noder already mentioned.
What I mean by actor driven is that the movie rests solely on the acting ability of the actors. The movie is solely dialogue, and I think the actors pulled it off well. Especially the facial expressions. If you've watched this movie once, watch it again, watching only the expressions of the actors and actresses. You can see what they are thinking and feeling through this medium alone. At the end, I could see the daughter's mind trying to figure out the puzzle of Joe's identity, while at the same time she is trying to conceal it because she is afraid of what she will find.
I think the movie makes a good point too: love is essentially selfish, although the writers of the movie chose to dance around the issue and try to conceal what they had revealed by having Anthony Hopkins explain what love is. Loving another person serves only one's self in the end, although the movie avoids the logical extreme of this argument, which is that humans are essentially selfish, but that is an understandable economic decision.
Of course, you, the reader who is reading this node, may well hate this movie. Ah well. I swear there is an objective basis to opinion, but I can't quite figure it out.