*warning* spoilers if you haven't seen the film.
Anyway.... I thought the beginning was pretty good, but most of the film after he met Jude Law was pretty dumb IMO (and I like pretty much every movie Jude Law is in). I didn't understand why Jude stuck with the kid for so long, among many other things. The plot got pretty predictable for awhile, however the film totally goes into uncharted territory once he meets the "blue fairy". I liked the whole "aliens trying to understand mankind" thing that was going on there, but the "we can clone someone, but only for a day" concept doesn't make any sense, especially by today's standards. Perhaps 10+ years ago (when Kubrick was toiling with how to make the film) it made more sense, but with our modern knowledge of cloning, that idea is totally bogus. That basically ruined the movie for me. I liked some of the ideas in it, however.
I hope someone can understand my ranting, because I sure can't!