Whatever can be said about this movie, the writer Luc Besson knows his sci-fi, but isn't above putting in some "this is over your head, so let your mind be blown" end-of-2001 (the movie, not the real year) style WTF effects. And here, I have to give it to Besson, it works. I mean, how else do you show what happens when someone becomes ten times (perhaps to some exponent) smarter? Beyond that, Besson shows that he's read Heinlein's Friday, and seen The Matirx, 2001: A Space Odyssey, and (perhaps most pointedly) Limitless. "Good artists copy, great artists steal" certainly fits here, though the theft is so light handed that it's more of artful pickpocketry.
Having said all that, what's the movie about? A 20-someting party girl played by Scarlett Johannsen gets unwillingly pulled into a drug ring and made a mule. A mule with a twist: the drugs are implanted into a pouch in her abdomen. Not ordinary drugs, these are a synthetic version of a natural compound that normally switches on babies' brains as they develop. When Lucy gets a swift kick to the ol' drug bag, it starts to leak into her system. She gets a mega-dose, and what ensues is not so much enhanced intelligence as more like a state approaching godhood. As you can imagine, subsequently very bad things happen to very bad people, Morgan Freeman's neuroscientist character gives her reassuring sage advice which she chooses to take, and all comes to a cosmically satisfactory conclusion.
OK, so at times there are the "we're effing with the ineffable" scenes of what this super-human is up to. Profound? Obscure crap? Or just the best that can be done in a movie? I'll pick doors #1 and #3, Monte. The story worked. Besson penned a sharp story then competently directed it, while Johanssen and Freeman and the rest of the cast pulled off some difficult acting to make it work, and the special effects team did their job in making it easy to suspend disbelief long enough to swallow the movie.
Three and a bit more stars out of Four. Worthwhile movie.