Johansson play the title character of 'Lucy', a woman who is unfortunate enough to end up being used in a drug deal, especially when the deal involves the drugs being stitched into her abdomen. During her captivity, she gets a little beaten up causing the drugs (which are a new thing on the market) to leak into her system and cause her brain to start using more than the mythical 10% people supposedly use. And so she seeks revenge as well as hunting down the other drug packages before her time is up. Morgan Freeman also pops up (because that's what Morgan Freeman does), making this a bit more reminiscent of 'Transcendence'.
While it may not be the smartest film around, it is at least an improvement over Luc Besson's last film as director (and that film was 'The Family'). The film shifts about quickly, and doesn't last too long - it's under 90 minutes (the film probably wouldn't have been able to make it last any longer than that, though it at least doesn't feel too stretched as it is). It kept me entertained.
If you're in the right mood, you should be able to enjoy this. If you're looking for something more than a disposable distraction, then you will be left wanting. I, personally, was fine with it.
SPOILERS!: As a side note, this film is actually a prequel to 'Bruce Almighty'. You see, at the end, Morgan Freeman gets hold of the secrets of the universe which he, obviously once the film finishes, keeps to himself and uses to take the place of 'God'.