If you can withstand 1) watching a film version of a play, featuring a lack of buildings, chalk outlines for streets and props, and basically nothing except actors in costume and a few chairs, doors, and windows; and 2) sitting through a ridiculous running time of nearly 3 hours, then you might just enjoy the twists and turns and sublime conclusion of this drama.The ultimate message here (and it goes without saying that this is a big spoiler) is that even small-town joes and janes have the potential to be, or, from another standpoint, already are, horrible and terribly immoral and twisted monsters on the inside, despite their docile appearances. The story follows in meticulous parallel arcs the moral downfalls (or, the revelation of existing immorality) of each character - in every case triggered in some way by Grace.
Grace is a complete foreigner in the town, and represents something new and unknown for the residents - and in what may be a basic pattern for children, first they are wary of the new toy, sort to speak; then they are interested and enthralled by it; and finally, after they see others' interest in it they begin to be selfish and covet it for themselves. Grace is also very tempting to the men (since there are slim pickings in Dogville...), and it is through the door of this sin we see them fall one after another like flies. The near-simultaneous avalanche nature of these moral failings is a bit unbelievable - but hey, at near 3 hours, it's a good thing they didn't stretch out the pacing any more than they did, right?
And the ending - now that's an ending! I think the conclusion made sitting through the entire film worthwhile. In the ending, of course, we learn not only Grace's secret, but via Daddy's speech, we learn in hindsight the psychopathology that has plagued Grace all along. After all, it was pretty hard not to question Grace's lack of actions in a number of scenes - when she was violated by a married man and then accused by the wife of instigating the adultery, Grace never said a word in her own defense. And why not say anything, we might ask? To avoid driving the married couple apart? To protect the public image of a man who is actually a dangerous rapist? The film posits the explanation that Grace pities these townspeoples and their flaws, and somehow reasons that they don't deserve to be punished for their transgressions. Meanwhile, she heartily accepts the yoke (actually a huge iron wheel chained to her neck) for things she hasn't done.
[SPOILERS below....]
Then, all of a sudden (and no hint how this happens), she has a brain aneurysm or something and realizes just how horribly these people have treated her. What follows is Grace going bananas, seizing power, taking revenge personally, and basically going apesh*t, killing everybody, and burning the town to the ground. A great whiz-bang, pull-out-the-stops, payoff ending. Is this technically a Happy Ending or not? Who cares? Kicks ass.