Why do you say save your money? What was wrong with it that its not worthy of seeing it in a theater?
Lucy was at best a graphics fest, and left out a number of potential threads that could have been used to wrap it up nicely. If you have a discount theater, go see it there, don't pay full price. (I watched it too, and was horribly disappointed.)
Towards the end of the movie Lucy was effectively a physical god, and there was no real competition to her. The only reason the crime boss got close in the end was because Lucy didn't use even a fraction of her power to simply splat him and his men.
A better ending would have been the crime boss thinking over, realizing where Lucy got the power from, and taking the drug himself. You then have a godwar, with Lucy as a party girl with extreme power on one side, and the crime boss with ruthlessness, focus, and creativity, but lower power on the other side. Lucy has to defend all of humanity, he just has to defend himself, and send off side strikes to keep her distracted (one example would be Tunguska). It would be a graphics fest, but it would put the hero (and all humanity) at risk.
There was also a comment about how Lucy was the name for the ancestor of all humanity, which would have been an interesting way for Scarlett Johnanson's character to end up. Powerless, alone, and the only solution is to change her body to fit history.
