The truth is, "Watermelon Man" really isn't a good movie, but the star's performance makes it fun at times, even if he is a bit hyperactive and exhausting.
Van Peebles may have been trying some breakthrough stuff and messing with the direction here and there, and I give him credit for trying, but in the end his direction really is not good and is very distractive at times. The color flashes, the use of music (though sometimes this works), the silent movie-type device and more, he's trying and while he definitely does something different, it's just, well, not good.
This film could have been a good fifteen or twenty minutes shorter, or at the very least some scenes could have been shorter and additional scenes to help the story could have been inserted.
Now of course, the whole thing with this film is to show how bad racism is, which only goes one way of course. But as time has passed, some things have shown not to work. Peebles tries to justify the black rioting (there seems to be a new black riot every day in the movie on TV) and the liberal wife makes excuses for it. I can't speak for the 1970 crowd, but that would not fly with most of today's crowd. Today's audience would very easily pick up that the racism is only one way, and a little too enthusiastic. A black man in a suit and tie is running down the street one morning, and almost instantly a huge crowd gathers around him to accuse him of stealing. C'mon.
And one thing that is shown in the film has proved to be all too true - when the liberal wife is confronted with an actual black man in her own home after Jeff turns black, she isn't so liberal anymore. Jeff even challenges her on it - where she answers she is still liberal, but only to a degree. This is the truth where countless (most? all?) liberals are concerned - they love to be supportive, but they suffer from "but not in my backyard" disease.
The film is a good viewing for one time only, just to see where Peebles' head was at, and to discuss all the flaws. And of course, for Godfrey's performance.
And I should say it's always good to see Mantan Moreland in anything, he's just great! But if Peebles was so concerned with racism, and the past injustices of Hollywood's typecasting of blacks, why did he put Moreland in a demeaning role of counterman in a diner (white boss of course), where he plays just another "yassuh, no suh" black guy? Even in Peebles' film, Mantan, even at old age, having very much paid his dues, couldn't catch a break.