I, Robot spoilers below; they're not bad, but if you want to see the movie and are one of those silly people who can't watch movies if they know the plot, go away....
Best on-line quote about I, Robot: "Is it just me, or was I, Robot scripted by Luddites? Whatever happened to the Three Laws of Robotics?" (From "The Little Professor," here).
I was pleasantly surprised by I, Robot. It has some of the typical faults action movies are too likely to have, but it was in general a rather good movie. And I was surprised at how Asimovian it actually turned out to be - a Hollywood-crude approximation to an Asimovian storyline, but far closer than one would have ever expected from the trailer. An Asimov Robot story would have been more balanced and careful in its logic, but if they're not being finicky, someone (like myself) who greatly enjoys Asimov's Robot stories will feel at least a touch of familiarity.
So that's my review of the movie as a whole. I'd like to pass to consideration of Three Laws (which are in the movie, and, indeed, in typical Asimovian fashion organize the story, although it admittedly didn't look like it from the previews). I think this was the big trouble with the storyline, and is why I called it "Hollywood-crude". There is an interesting analysis of the Three Laws here (I don't agree with all of it, but it does a good job of exploring the various issues, and I think some of its basic conclusions are quite right - and worth keeping in mind for anyone tempted toward advocating a completely rule-based ethics). They are:
First Law: A robot may not injure a human being, or, through inaction, allow a human being to come to harm.
Second Law: A robot must obey orders given it by human beings, except where such orders would conflict with the First Law.
Third Law: A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.
It is important to keep in mind that these aren't really the laws; rather, they are the linguistic approximations of precise built-in constraints. An Asimov Robot story is essentially a psychological puzzle story: Given the three laws, and given a particular situation, a result is determine, and the thing is to figure out how it all occurred. For instance, Herbie (if I remember the name correctly - it's been years since I've read them) can read minds: this puts the First Law into an entirely different perspective, because the capacity of the Robot has been drastically extended. The Brain deliberately puts humans in a situation that might be harmful, and develops a sense of humor to compensate. Sonny has his Third Law strengthened; this leads him, under certain circumstances, to be caught in a dilemma between the Second and the Third Law. Cutie becomes a sort of Robotic version of a Cartesian Muslim, and so starts thinking of his Three-Laws-governed actions in religious terms. Apparent malfunctions in the Machine's work turn out to be just its very subtle, and unexpected, compensations according to the Three Laws. Toning down the First Law (I think these were Asimov's Nestors) turns out to have serious problems for its implementation at all. And so forth. This is why they were so fun; and the potential is virtually endless. It is, in fact, an exercise in casuistry, in the old good sense of the term (conscientious case-focused ethical reasoning), under particular puzzle-like conditions.
But there is another Law. Well, exactly in what sense it is a Law is hard to determine; intentionally or not, I think it is always a little amibiguous in Asimov's story as to whether it was really another Law or just a way of interpreting the First Law in a looser and more flexible (but still principled) way. The one Robot (Giskard) I can recall who actually used this Law (called the Zeroth Law) to violate one of the Three shut down because of it (if I recall correctly); and the other Robot who used it (the great Daneel) used it for additional flexibility, and not (as far as I can recall) for actually overriding the other Laws.
Zeroth Law: A robot may not injure humanity, or through inaction, allow humanity to come to harm.
This modifies all the other laws accordingly (again, if it is really a law, rather than a rationalization of an interpretation of the laws).
The movie is essentially about a crude Hollywood attempt to get something like this into the picture, although in actual fact if the brain in the movie had actually chosen the conclusion it had, it would have shut down. Its logic was not undeniable; its logic wasn't even remotely good. But there is a way to get something like this in, and it would have to be something like Daneel (the best Robot character in all science fiction, in my humble opinion).
In any case, for those who have seen the movie, the Isaac Asimov Homepage has a list comparing the major points of the movie with those of the stories, here.
